One-county state wins

This list seeks to enumerate all the instances in which one county handed a state to a presidential nominee from 1880 on. It also lists the counties, each of which individually handed a given state to a nominee in a given election. Sometimes (often, actually), there is more than one county which gave the nominee a larger raw-vote margin than he or she won the state by. If there is only one, that may be significant, as the Orange County Register alluded to after the 2016 election:

As of this writing, Clinton’s lead in the popular vote nationwide was 1.7 million. Clinton’s lead in California was 3.5 million.

That means, when all the votes are counted and Clinton’s popular-vote edge is official, it probably will in a manner of speaking have hinged entirely on the results in California.

This is rare: In the Bush-Gore election, four states gave Gore vote margins larger than his 543,895-vote national margin. The last time a single state’s voting accounted for a candidate’s national vote margin was 1888, which happens to be the last election before Bush-Gore to see an Electoral College/popular vote split. Grover Cleveland received 90,596 more votes than Benjamin Harrison nationwide, and for that Cleveland could thank the 146,461-vote margin he received in Texas.

When only one county accounted for a nominee's statewide margin, it will be bolded. 

WHIGS
1832
Delaware (1.98%): Sussex

REPUBLICANS
1880
Oregon (1.63%): Marion

other close states:
Indiana (1.41%) (unknown)
New York (1.91%) (unknown)
Connecticut (2.00%) (unknown)

1884
none known

other close states:
Michigan (0.82%)
Illinois (3.73%) (unknown)

1888
Indiana (0.44%): Wayne, Randolph

other close states:
New York (1.09%)
Ohio (2.33%)
New Hampshire (2.50%)
California (2.82%)
Illinois (2.96%) (unknown)

1892
Ohio (0.13%): Warren, Trumbull, Scioto, Meigs, Lucas, Lorain, Logan, Lawrence, Lake, Jefferson, Hamilton, Greene, Geauga, Gallia, Columbiana, Clinton, Athens, Ashtabula

other close states:
Nebraska (2.04%)
Montana (2.66%)

1896
Kentucky (0.06%): Jefferson, Whitley, Pulaski, Campbell, Knox, Christian, Jackson, Bell, Fayette, Clay, Harlan, Laurel, Lewis, Boyd, Leslie, Johnson, Monroe, Owsley, Carter, Butler, Clinton, Rockcastle, Casey, Cumberland, Muhlenberg, Martin, Perry, Boyle, Greenup, Russell, Letcher, Garrard, Bourbon, Madison, Magoffin, Lee
California (0.64%): Alameda
Oregon (2.09%): Multnomah

other close states:
Indiana (2.85%)

1900
none known

other close states:
Utah (2.29%)
Nebraska (3.24%)
Indiana (3.99%)

1904
Maryland (0.02%): Calvert, Somerset, Charles, Washington, Prince George's, Dorchester, Frederick, Garrett, Allegany

other close states:
Missouri (3.90%)

1908
Missouri (0.09%): St Louis City, St Louis County
Maryland (0.25%): Frederick, Garrett, Baltimore City

other close states:
Indiana (1.49%)

1912
(none)

other close states:
Vermont (1.91%)

1916
Minnesota (0.10%): Blue Earth, Brown, Carver, Chisago, Cottonwood, Faribault, Fillmore, Freeborn, Goodhue, Houston, Lac qui Parle, McLeod, Mower, Nicollet, Otter Tail, Redwood, Renville, Rock, Sibley, Stearns, Washington, Watonwan, Wright
West Virginia (0.94%): McDowell
Delaware (2.43%): New Castle

other close states:
Indiana (0.97%)
Oregon (2.57%)
Connecticut (3.15%)
South Dakota (3.90%)
Massachusetts (3.93%)

1920
(none)

other close states:
Tennessee (3.10%)

1924
North Dakota (2.52%): Cass

other close states:
Kentucky (2.96%)
Maryland (3.9991%)

1928
(none)

other close states:
New York (2.35%)
Texas (3.67%)

1932
Connecticut (1.14%): Fairfield
New Hampshire (1.43%): Rockingham
Delaware (2.44%): New Castle

other close states:
(none)

1936
(none)

other close states:
(none)

1940
Michigan (0.33%): Allegan, Huron, Ingham, Jackson, Kalamazoo, Lenawee, Sanilac, Washtenaw

other close states:
Indiana (1.42%)
Maine (2.33%)
Colorado (2.55)

1944
(none)

other close states:
Ohio (0.37%)
Wisconsin (1.80%)
Wyoming (2.47%)

1948
New York (0.98%): Westchester, Nassau
Delaware (1.28%): Sussex
Maryland (1.39%): Baltimore County, Montgomery
Connecticut (1.64%): Fairfield

other close states:
Indiana (0.80%)
Michigan (1.67%)
Oregon (3.39%)

1952
Tennessee (0.27%): Hamblen, Hawkins, Johnson, Greene, Jefferson, Sullivan, Cocke, Hamilton, Sevier, Carter, Blount, Washington, Knox
Rhode Island (1.84%): Kent

other close states:
Missouri (1.56%)
Delaware (3.88%)

1956
Tennessee (0.61%): Sevier, Hamilton, Blount, Washington, Carter, Knox

other close states:
(none)

1960
Montana (2.50%): Yellowstone
Alaska (1.88%): Anchorage
California (0.55%): Orange, San Diego

other close states:
Washington (2.41%)
Florida (3.03%)
Wisconsin (3.72%)

(note: Alaska does not report election results by borough. This is an estimate based on cinyc's estimate of how Alaska's boroughs have voted in every election. Cinyc's estimate of Nixon's margin in Anchorage in 1960 was 7.4%; in order for Anchorage not to have handed the state to him, Nixon's margin there would have had to have been under 5.5%.)

1964
Arizona (1.00%): Maricopa

other close states:
(none)

1968
New Jersey (2.13%): Bergen

other close states:
Missouri (1.13%)
Ohio (2.28%)
Alaska (2.64%)
Illinois (2.92%)
California (3.08%)
Delaware (3.51%)
Wisconsin (3.62%)
Tennessee (3.83%)

1972
(none)

other close states:
(none)

1976
Oregon (0.16%): Washington, Marion, Malheur, Klamath, Clackamas, Benton
Maine (0.84%): Hancock, Penobscot
Oklahoma (1.21%): Oklahoma, Tulsa
Virginia (1.33%): Henrico
California (1.78%): Orange
Illinois (1.97%): DuPage
New Mexico (2.47%): Bernalillo

other close states:
Iowa (1.01%)
South Dakota (1.48%)
New Jersey (2.16%)
Washington (3.88%)

1980
Massachusetts (0.15%): Plymouth, Barnstable, Norfolk, Essex
Tennessee (0.29%): Greene, Carter, Washington, Sevier, Blount, Hamilton, Knox
Arkansas (0.61%): Washington, Sebastian, Benton
Alabama (1.30%): Jefferson, Mobile
South Carolina (1.53%): Lexington, Greenville

other close states:
Mississippi (1.32%)
Kentucky (1.46%)
North Carolina (2.12%)
Delaware (2.33%)
New York (2.67%)
Maine (3.36%)

1984
(none)

other close states:
Massachusetts (2.79%)
Rhode Island (3.65%)

1988
Illinois (2.09%): DuPage

other close states:
Pennsylvania (2.32%)
Maryland (2.91%)
Vermont (3.52%)
California (3.57%)
Missouri (3.98%)

1992
Arizona (1.95%): Maricopa

other close states:
North Carolina (0.79%)
Florida (1.89%)
Texas (3.48%)
South Dakota (3.52%)

1996
Georgia (1.17%): Cobb, Gwinnett
Colorado (1.37%): El Paso

other close states:
Virginia (1.96%)
Montana (2.88%)
South Dakota (3.46%)

2000
Florida (0.01%): Baker, Bay, Bradford, Brevard, Calhoun, Charlotte, Citrus, Clay, Collier, Columbia, Desoto, Dixie, Duval, Escambia, Gilchrist, Gulf, Hardee, Hendry, Highlands, Hillsborough, Holmes, Indian River, Jackson, Lafayette, Lake, Lee, Levy, Manatee, Marion, Martin, Nassau, Okaloosa, Polk, Putnam, Santa Rosa, Sarasota, Seminole, St Johns, Sumter, Suwannee, Taylor, Union, Wakulla, Walton, Washington

other close states:
New Hampshire (1.27%)
Missouri (3.34%)
Ohio (3.51%)
Nevada (3.55%)
Tennessee (3.86%)

2004
Iowa (0.67%): Sioux
New Mexico (0.79%): San Juan, Otero, Chaves, Lea, Curry, Eddy

other close states:
Ohio (2.10%)
Nevada (2.59%)

2008
Missouri (0.13%): Barry, Butler, Camden, Cape Girardeau, Cass, Christian, Cole, Franklin, Greene, Howell, Jasper, Laclede, Lawrence, Newton, Pettis, Phelps, Polk, Pulaski, Scott, St Charles, Stoddard, Stone, Taney, Webster

other close states:
Montana (2.26%)

2012
(none)

other close states:
North Carolina (2.04%)

2016
Michigan (0.23%): Allegan, Jackson, Lapeer, Livingston, Macomb, Monroe, Ottawa, St Clair
Pennsylvania (0.71%): Westmoreland, Lancaster, York
Wisconsin (0.77%): Washington, Waukesha

other close states:
Florida (1.20%)
Arizona (3.55%)
North Carolina (3.66%)

2020
(none)

other close states:
North Carolina (1.34%)
Florida (3.36%)

DEMOCRATS
1852
Delaware (0.19%): New Castle

1880
California (0.06%): Mariposa, Kern, San Benito, Merced, Lake, Sonoma, Mendocino, Tulare, Stanislaus, Fresno, Colusa, San Francisco

other close states:
New Jersey (0.82%) (unknown)
North Carolina (3.45%)
Delaware (3.87%) (unknown)

1884
New York (0.10%): Manhattan, Brooklyn, Queens, Staten Island, Westchester, Otsego, Schoharie
Connecticut (0.94%): Hartford

other close states:
Indiana (1.32%) (unknown)
New Jersey (1.67%) (unknown)
Virginia (2.15%)
West Virginia (3.19%) (unknown)
Tennessee (3.72%)

1888
Connecticut (0.22%): Hartford
Virginia (0.53%): Radford City

other close states:
West Virginia (0.32%) (unknown)
New Jersey (2.35%) (unknown)
Maryland (2.94%) (unknown)

1892
California (0.05%): Colusa, Stanislaus, San Francisco, Modoc, Glenn, Yolo, Merced, Kern, Tuolumne, Sonoma, Mendocino, San Joaquin, Fresno, Tulare
Illinois (3.09%): Cook
New York (3.41%): Manhattan

other close states:
Indiana (1.29%)
Delaware (1.35%) (unknown)
Wisconsin (1.68%)
West Virginia (2.44%) (unknown)
Connecticut (3.26%)

1896
South Dakota (0.22%): Minnehaha, Pennington, Brown, Meade, Lawrence, Union, Moody, McCook, Brule, Hanson
Wyoming (3.74%): Uinta

other close states:
Kansas (3.69%)

1900
(none known)

other close states:
Kentucky (1.71%)
Idaho (3.83%)

1904
(none known)

other close states:
Kentucky (2.69%)

1908
Colorado (1.12%): Denver
Nevada (1.78%): Esmeralda

other close states:
Kentucky (1.71%)

1912
Wyoming (1.78%): Sheridan
Rhode Island (3.48%): Providence
Massachusetts (3.58%): Suffolk

other close states:
Idaho (1.05%)
Illinois (1.62%)
Maine (2.02%)
New Hampshire (2.04%)
Connecticut (3.28%)

1916
New Hampshire (0.06%): Coös, Hillsborough
California (0.38%): Kern, Sacramento, San Francisco

other close states:
North Dakota (1.50%)
New Mexico (3.56%)
Missouri (3.65%)

1920
Kentucky (0.44%): Graves, Kenton

other close states:
(none)

1924
(none)

other close states:
(none)

1928
Rhode Island (0.61%): Providence
Massachusetts (1.09%): Suffolk

other close states:
Alabama (2.84%)

1932
New Jersey (1.90%): Hudson
Massachusetts (4.00%): Suffolk
Rhode Island (11.77%): Providence

other close states:
Ohio (2.85%)

1936
New Hampshire (1.75%): Hillsborough

other close states:
(none)

1940
Wisconsin (1.82%): Milwaukee
Illinois (2.43%): Cook
New York (3.56%): Brooklyn
New Jersey (3.62%): Hudson
New Hampshire (6.44%): Hillsborough
Rhode Island (13.56%): Providence

other close states:
Minnesota (3.83%)

1944
Michigan (1.02%): Wayne
New Jersey (1.35%): Hudson, Camden
Pennsylvania (2.78%): Philadelphia
Missouri (2.94%): St Louis City
Illinois (3.47%): Cook
Maryland (3.70%): Baltimore City
New Hampshire (4.24%): Hillsborough
Oregon (4.85%): Multnomah
New York (5.01%): Brooklyn
Delaware (9.11%): New Castle

other close states:
Idaho (3.49%)

1948
Ohio (0.24%): Belmont, Cuyahoga, Jefferson, Lucas, Mahoning, Montgomery, Summit, Trumbull
California (0.44%): Sacramento
Illinois (0.84%): Cook
Nevada (3.11%): Clark
Rhode Island (16.15%): Providence

other close states:
Idaho (2.73%)
Iowa (2.73%)

1952
Kentucky (0.07%): Graves, Elliott, Morgan, Knott, Ballard, Breathitt, Bullitt, Calloway, Carlisle, Barren, Carroll, Clark, Christian, Floyd, Franklin, Fulton, Gallatin, Grant, Harrison, Henry, Hickman, Hopkins, Logan, Marion, Marshall, McCracken, Meade, Owen, Pike, Simpson, Todd, Trigg, Trimble, Union, Webster, Anderson, Boyle, Bourbon
South Carolina (1.44%): Anderson, Spartanburg

other close states:
West Virginia (3.85%)

1956
Missouri (0.22%): Jackson, New Madrid, Pemiscot, St Louis City

other close states:
North Carolina (1.33%)

1960
Hawaii (0.06%): Oahu
Illinois (0.18%): Cook, St Clair, Madison
Missouri (0.52%): St Louis City, Jackson
New Mexico (0.74%): Rio Arriba, Santa Fe
New Jersey (0.80%): Essex, Hudson, Mercer, Middlesex
Minnesota (1.43%): Ramsey, St Louis County
Delaware (1.64%): New Castle
Michigan (2.01%): Wayne
Pennsylvania (2.32%): Philadelphia
Nevada (2.32%): Clark
South Carolina (2.48%): Anderson
Maryland (7.22%): Baltimore City

other close states:
Texas (2.00%)

1964
Idaho (1.83%): Bannock
Florida (2.30%): Dade

other close states:
(none)

1968
Maryland (1.65%): Baltimore City
Pennsylvania (3.57%): Philadelphia
Michigan (6.73%): Wayne

other close states:
Texas (1.27%)
Washington (2.11%)

1972
(none)

other close states:
(none)

1976
Ohio (0.27%): Cuyahoga, Lorain, Lucas, Mahoning, Summit, Trumbull
Wisconsin (1.67%): Milwaukee
Pennsylvania (2.67%): Philadelphia
Maryland (6.08%): Baltimore City

other close states:
Mississippi (1.88%)
Hawaii (2.53%)
Texas (3.17%)
Missouri (3.63%)

1980
Maryland (2.96%): Baltimore City

other close states:
Hawaii (1.90%)
Minnesota (3.94%)

1984
Minnesota (0.18%): Ramsey, St Louis County, Hennepin, Mower, Carlton

other close states:
(none)

1988
Washington (1.59%): King
Wisconsin (3.62%): Milwaukee
New York (4.10%): Manhattan
Oregon (4.67%): Multnomah

other close states:
(none)

1992
Georgia (0.59%): DeKalb, Fulton
Ohio (1.83%): Cuyahoga
Nevada (2.63%): Clark
Delaware (8.19%): New Castle

other close states:
New Hampshire (1.22%)
New Jersey (2.37%)
Montana (2.51%)
Kentucky (3.21%)

1996
Kentucky (0.96%): Jefferson
Nevada (1.02%): Clark
Arizona (2.23%): Pima

other close states:
Tennessee (2.41%)

2000
New Mexico (0.06%): Bernalillo, San Miguel, Taos, Rio Arriba, Santa Fe, Mora, Guadalupe, McKinley, Cibola, Grant, Doña Ana
Wisconsin (0.22%): Dane, Douglas, Milwaukee, Rock
Iowa (0.32%): Black Hawk, Dubuque, Johnson, Linn, Polk
Oregon (0.44%): Lane, Multnomah
Minnesota (2.40%): Hennepin
Pennsylvania (4.17%): Philadelphia
Michigan (5.13%): Wayne
Washington (5.58%): King
Illinois (12.01%): Cook
Delaware (13.06%): New Castle

other close states:
(none)

2004
Wisconsin (0.38%): Dane, Milwaukee, Rock
Pennsylvania (2.50%): Philadelphia
Michigan (3.42%): Wayne
Minnesota (3.48%): Hennepin
Oregon (4.16%): Multnomah
Washington (7.17%): King
Delaware (7.60%): New Castle
Illinois (10.34%): Cook

other close states:
New Hampshire (1.37%)

2008
North Carolina (0.32%): Buncombe, Cumberland, Durham, Forsyth, Guilford, Mecklenburg, Orange, Wake
Indiana (1.03%): Lake, Marion
Florida (2.82%): Broward
Nevada (12.50%): Clark
Delaware (24.98%): New Castle

other close states:
(none) (Ohio [margin 4.59%] was the closest non-one-county-win)

2012
Florida (0.87%): Broward, Dade, Orange, Palm Beach
Ohio (2.98%): Cuyahoga
Colorado (5.36%): Denver
Pennsylvania (5.38%): Philadelphia
Nevada (6.88%): Clark
Illinois (16.84%): Cook
Delaware (18.36%): New Castle

other close states:
Virginia (3.88%)

2016
New Hampshire (0.37%): Cheshire, Grafton, Sullivan
Minnesota (1.51%): Hennepin, Ramsey
Nevada (2.42%): Clark
Maine (2.96%): Cumberland
Colorado (4.89%): Denver
Oregon (10.98%): Multnomah
Delaware (11.38%): New Castle
Illinois (16.88%): Cook

other close states:
(none) (Virginia [margin 5.32%] was the closest non-one-county win)

2020
Georgia (0.24%): DeKalb, Fulton, Clayton, Gwinnett, Cobb, Richmond, Henry, Chatham, Clarke, Muscogee, Rockdale, Douglas, Bibb, Dougherty
Arizona (0.31%): Apache, Coconino, Maricopa, Pima
Wisconsin (0.63%): Milwaukee, Dane
Pennsylvania (1.17%): Philadelphia, Allegheny, Montgomery, Delaware
Nevada (2.39%): Clark
Michigan (2.78%): Wayne
Minnesota (7.11%): Hennepin
Maine (9.07%): Cumberland
Illinois (16.99%): Cook
Delaware (18.97%): New Castle

other close states:
(none)

---

The largest margin whereby a Republican has won a state, such that the entire margin was accounted for in one county, as far as I know, was 2.52% (North Dakota in 1924)--and that was Coolidge's margin over Progressive (and former Republican) nominee Robert La Follette. The next-largest, and the largest in which the Democrat came in second, was 2.50% (Montana in 1960), followed by 2.47% (New Mexico in 1976), 2.44% (Delaware in 1932), 2.43% (Delaware in 1916), 2.13% (New Jersey in 1968), and 2.09% (Illinois in 1988 and Oregon in 1896). 2.13% is the largest such margin I know of in a mega-state (one with 14 or more electoral votes at the time of the election).

On the other hand, as early as at least 1892, Democrats were winning multiple states by more than 3% such that the margin was accounted for in one county. Even when the party took a more rural turn with Bryan and Wilson, each won at least one state by more than 3% in such a manner (in 1896 and 1912). From 1932 on, Democrats were regularly winning states by non-close margins in such a manner that the margin was accounted for in one county--although, curiously, Bill Clinton's re-election in 1996 represented a respite from this tendency: his largest one-county margin was just 2.23%, and the smallest margin he won a state such that no one county accounted for the margin was 2.41%, which has remained unequalled since (apart from Kerry's 1.37% win in New Hampshire in 2004). But 1996 was a departure from a norm. 

That said, Democrats appear to be winning ever larger margins that can be accounted for in one county, whereas Republicans are winning ever smaller margins that can't be so accounted. 2000 was the first time that a Democrat (or any nominee) won a mega-state by more than 10% in one county (previously, they had carried only Rhode Island in this manner). In 2008, Obama set a new record for the largest margin whereby a nominee has won a state such that the margin was accounted for in one county (his 24.98% margin in Delaware that year beating out Truman's 16.15% margin in Rhode Island). In 2012, he won Illinois (a mega-state with 102 counties) by a greater percent margin than Truman won Rhode Island by, his entire margin in the state coming from Cook County, a feat that was replicated in 2016 and 2020. On the other hand, Republicans have not won a state by more than 2% in such a way that the margin came entirely from one county since 1988, nor a state by more than 1% in such a way since 1996. (That said, no Republican since 1992 has managed to replicate Bush Sr's feat in 1992 of winning North Carolina by less than 1% in such a way that no one county accounted for his margin.)

There are some instances on which Republicans have come close to winning a state by a larger margin than 2.5% (in some cases considerably larger) in one county:

In 1920, Harding won New Castle County, Delaware by 13.3% of Delaware's total vote, and won Delaware by 13.64%.

In 1924, Coolidge won New Castle County, Delaware by 19.4% of Delaware's total vote, and won Delaware by 20.9%.

In 1960, Nixon won Maricopa County, Arizona by 10.1% of Arizona's total vote, and won Arizona by 11.16%.

In 1960, Nixon won Pinellas County, Florida by 2.83% of Florida's total vote, and won Florida by 3.02%.

In 1976, Ford won Maricopa County, Arizona by 15.3% of Arizona's total vote, and won Arizona by 16.57%.

In 1988, Bush Sr won Orange County, California by 3.2% of California's total vote, and won California by 3.57%.

In 2000, George W. Bush won Maricopa County, Arizona by 6.1% of Arizona's total vote, and won Arizona by 6.29%.

In 2004, George W. Bush won El Paso County, Colorado by 3.93% of Colorado's total vote, and won Colorado by 4.67%.

But, especially considering how few counties some states have and how top-heavily some states' populations are clustered in one county, it is still surprising that a Republican one-county win has never (to my knowledge) gone over 2.52%. This seems to suggest that, as a general rule, counties that are both large and strongly Republican have historically been less at odds with their overall states, than counties that are both large and strongly Democratic have been.

2008 was the first time a Dole county delivered its state to a Democrat (Wake and Forsyth, NC), followed by Orange, FL in 2012, and Cobb, Gwinnett, Henry, Rockdale, and Douglas, GA, and Maricopa, AZ in 2020. 2016 was the first time a Mondale county delivered its state to a Republican (Westmoreland, PA). The most recently that a county that voted for Trump (in 2020) delivered its state to a Democrat was 2000 (Dubuque, IA). The most recently that a county that voted for Biden delivered its state to a Republican was also 2000 (when Hillsborough, Seminole, and Duval, FL all did so), but of course the margin in Florida was tiny that year, and a large number of counties accounted for Bush's margin in the state. The next-most recently was 1996, when Cobb and Gwinnett each handed Georgia to Bob Dole. (The next-most recently for the other way around was 1984, when Mower County, MN handed the state to Mondale, followed by 1976, when Lorain, Mahoning, and Trumbull Counties, OH each handed Ohio to Carter.)

---

Here are some other instances of one-county wins in other statewide races:

California governorial, 1982 (Deukmejian 49.28%-Bradley 48.09%): Orange

Virginia governorial, 2013 (McAuliffe 47.75%-Cuccinelli 45.23%): Fairfax

Massachusetts governorial, 2014 (Baker 48.39%-Coakley 46.54%): Worcester 

Kentucky governorial, 2019 (Beshear 49.20%-Bevin 48.83%): Jefferson, Fayette, Franklin