Wallace's top three counties in every state

Bold indicates that Wallace came in first in the county. Italics indicates Wallace came in second. If Wallace's vote share was a majority (rather than a plurality), it is also bolded; if Wallace carried the state, its name is bolded.

Alabama
1. Geneva: 91.73%
2. Lamar: 88.25%
3. Covington: 86.98%

Mississippi
1. George: 91.20%
2. Calhoun: 87.80%
3. Smith: 84.70%

Florida
1. Holmes: 87.21%
2. Liberty: 76.95%
3. Lafayette: 76.17%

Georgia
1. Echols: 83.02%
2. Miller: 81.60%
3. Seminole: 77.10%

Louisiana
1. Livingston: 80.85%
2. West Carroll: 78.48%
3. Franklin: 75.68%

Arkansas
1. Cleveland: 70.89%
2. Grant: 59.73%
3. Prairie: 56.23%

Tennessee
1. Crockett: 63.67%
2. Cheatham: 63.31%
3. Moore: 60.03%

North Carolina
1. Currituck: 57.19%
2. Greene: 56.80%
3. Franklin: 56.64%

South Carolina
1. Abbeville: 54.82%
2. Cherokee: 53.77%
3. Anderson: 53.23%

Virginia
1. Charlotte: 50.72%
2. Pittsylvania: 46.77%
3. Halifax: 46.53%

Texas
1. Loving: 49.38%
2. Shelby: 47.45%
3. San Augustine: 46.22%

Kentucky
1. Todd: 43.13%
2. Hickman: 42.96%
3. Fulton: 39.97%

Oklahoma
1. Atoka: 38.92%
2. Pushmataha: 34.38%
3. McCurtain: 33.41%

Missouri
1. Pemiscot: 37.71%
2. New Madrid: 31.42%
3. Mississippi: 29.72%

Maryland
1. Dorchester: 31.81%
2. St Mary's: 27.76%
3. Calvert: 27.00%

Nevada
1. Esmeralda: 27.48%
2. Mineral: 24.40%
3. Nye: 24.14%

Ohio
1. Warren: 25.35%
2. Clermont: 24.15%
3. Brown: 21.73%

Idaho
1. Custer: 22.98%
2. Lemhi: 21.04%
3. Gooding: 20.36%

Illinois
1. Alexander: 20.81%
2. Pulaski: 17.59%
3. St Clair: 15.13%

New Mexico
1. Lea: 19.67%
2. Curry: 17.03%
3. Hidalgo: 16.65%

Indiana
1. Morgan: 19.36%
2. Porter: 18.80%
3. Clark: 18.53%

Delaware
1. Kent: 19.09%
2. Sussex: 17.47%
3. New Castle: 11.46%

Colorado
1. Teller: 18.07%
2. Dolores: 17.70%
3. San Juan: 16.48%

Arizona
1. Graham: 17.43%
2. Navajo: 15.96%
3. Cochise: 14.32%

Kansas
1. Morton: 17.36%
2. Wyandotte: 16.64%
3. Jefferson: 15.75%

Nebraska
1. Sarpy: 16.96%
2. Banner: 14.05%
3. Boyd: 12.77%

Utah
1. Washington: 15.92%
2. Kane: 15.33%
3. Daggett: 14.43%

New Jersey
1. Gloucester: 15.46%
2. Salem: 13.89%
3. Mercer: 12.83%

Michigan
1. Cass: 15.14%
2. Genesee: 14.96%
3. Berrien: 14.83%

Pennsylvania
1. Fulton: 14.90%
2. Franklin: 12.95%
3. Perry: 11.26%

Wisconsin
1. Taylor: 13.85%
2. Forest: 13.08%
3. Adams: 12.22%

Washington
1. Franklin: 13.57%
2. Ferry: 13.12%
3. Stevens: 13.03%

Wyoming
1. Sublette: 13.39%
2. Campbell: 11.37%
3. Natrona: 11.22%

Montana
1. Garfield: 13.27%
2. Lincoln: 13.17%
3. Ravalli: 11.86%

Oregon
1. Douglas: 13.16%
2. Josephine: 12.27%
3. Malheur: 10.67%

California
1. Trinity: 13.06%
2. Amador: 12.24%
3. Yuba: 11.62%

South Dakota
1. Jackson: 11.60%
2. Faulk: 9.88%
3. Custer: 9.40%

Iowa
1. Mills: 11.39%
2. Pottawattamie: 9.71%
3. Fremont: 9.27%

North Dakota
1. Billings: 10.82%
2. Emmons: 10.16%
3. Kidder: 9.86%

New York
1. Putnam: 9.82%
2. Staten Island: 9.22%
3. Suffolk: 8.35%

Minnesota
1. Mahnomen: 7.72%
2. Isanti: 7.12%
3. Marshall: 7.02%

Massachusetts
1. Suffolk: 5.62%
2. Hampden: 5.53%
3. Hampshire: 5.10%

Rhode Island
1. Washington: 4.80%
2. Kent: 4.151%
3. Providence: 4.146%

Vermont
1. Grand Isle: 4.68%
2. Orleans: 3.78%
3. Bennington: 3.51%

New Hampshire
1. Hillsborough: 4.59%
2. Rockingham: 4.45%
3. Carroll: 3.74%

Maine
1. Waldo: 2.73%
2. Lincoln: 2.40%
3. Piscataquis: 2.28%

Data for four states were unavailable. Of those four, Wallace's best was actually Alaska, where he got 12.07%. Per this map, Alaska appears to be the only one where Wallace might have received over 25% in a county equivalent. According to RRH Elections' estimate, Wallace's top borough result in Alaska was 22.3%, in Denali.

If we assume that is the case, then it would appear that these are the only states where Wallace got over 25% in at least one county. These are the only states where Wallace got over 25% in multiple counties. Six counties in Maryland gave Wallace over 25% of the vote (number is number of votes cast in 1968):

Dorchester: 31.81% (10,114)
St Mary's: 27.76% (9,175)
Calvert: 27.00% (5,449)
Somerset: 26.95% (7,047)
Charles: 26.30% (12,065)
Worcester: 25.09% (7,458)

In five of the six, Wallace did better than he did in Warren County, Ohio, one of the two counties outside the South where he got over a quarter of the vote (in this case, 25.35%). Dorchester, St Mary's, Calvert, Somerset, and Charles Counties (the counties in Maryland where Wallace ran ahead of his showing in Warren County, Ohio) collectively cast 43,850 votes in 1968; Warren County cast 26,014. Wallace outperformed his showing in Esmeralda County, Nevada in only two counties in Maryland, but Esmeralda County cast only 353 votes in 1968.

Additionally, 30% is something of an arbitrary threshold, but if one considers Maryland outside the South, then it was the only state outside the South where a county cast over 30% of its vote for Wallace.

(In Missouri, incidentally, Wallace got above 25% of the vote only in the three listed counties--his fourth-best showing was in Dunklin County, where he got 23.54%. Pemiscot, New Madrid, and Mississippi collectively cast 22,617 votes in 1968. Hence, Wallace did better in Dorchester County than he did in any county in Missouri save Pemiscot, and better in seven counties in Maryland [having gotten 23.60% in Wicomico] than in all but three counties in Missouri.) 

Wallace's seven best counties in Missouri (Pemiscot, New Madrid, Mississippi, Dunklin, Scott, Butler, and Stoddard) all lie in the Mississippi Embayment region of the state. His best county outside that region was Jefferson, where he got 19.69% of the vote. His best county north of the Missouri River (in Missouri)--and his ninth-best in the state overall--was St Charles County (where he got 19.39%), a county that lies in the Missouri Rhineland region and was historically Republican dating back to 1864 (having voted Democratic only in 1872, 1876, 1932, 1936, 1948, 1960, and 1964 since 1860). His best county in 'Little Dixie' (and his second-best county in the state north of the Missouri River) was Lincoln County, where he got 17.01% (and which Nixon simultaneously became the first Republican since 1868 to carry). 

As for Florida, George Wallace carried 43 counties in the state, out of 67 total. He carried Florida's fourth-largest county, Duval County (which cast 166,978 votes). Although Wallace dominated northern Florida, his counties were found throughout the state, including along the I-4 Corridor (Polk County) and in the Florida Heartland (DeSoto, Glades, Hardee, Hendry, and Okeechobee).