Named after Thomas Jefferson, except where noted.

Jefferson County

1. One of 67 counties in Alabama, United States. County seat: Birmingham.
2. One of 75 counties in Arkansas, United States. County seat: Pine Bluff.
3. One of 64 counties in Colorado, United States. County seat: Golden.
4. One of 67 counties in Florida, United States. County seat: Monticello.
5. One of 159 counties in Georgia, United States. County seat: Louisville.
6. One of 44 counties in Idaho, United States. County seat: Rigby.
7. One of 102 counties Illinois, United States. County seat: Mount Vernon.
8. One of 92 counties in Indiana, United States. County seat: Madison.
9. One of 99 counties in Iowa United States. County seat: Fairfield.
10. One of 105 counties in Kansas, United States. County seat: Oskaloosa.
11. One of 120 counties in Kentucky, United States. County seat: Louisville.
    • 2025 July 22, Connor N. Smith, Mason Brighton, “Louisville drops sanctuary city status after DOJ pressure”, in Spectrum News‎^[1], archived from the original on 20 August 2025:

      The U.S. Department of Homeland Security announced on May 29 that Louisville was one of more than 600 municipalities across the U.S. accused of obstructing immigration enforcement. The federal government called these locations “sanctuary jurisdictions,” alleging they were undermining the rule of law. Four Kentucky counties also made the list: Campbell, Franklin, Jefferson and Scott.

12. One of 82 counties in Mississippi, United States. County seat: Fayette.
13. One of 114 counties in Missouri, United States. County seat: Hillsboro.
14. One of 56 counties in Montana, United States. County seat: Boulder.
15. One of 93 counties in Nebraska, United States. County seat: Fairbury.
16. One of 62 counties in New York, United States. County seat: Watertown.
17. One of 88 counties in Ohio, United States. County seat: Steubenville.
18. One of 77 counties in Oklahoma, United States. County seat: Waurika.
19. One of 36 counties in Oregon, United States. County seat: Madras. Named after Mount Jefferson (Oregon).
20. One of 67 counties in Pennsylvania, United States. County seat: Brookville.
21. One of 95 counties in Tennessee, United States. County seat: Dandridge.
22. One of 254 counties in Texas, United States. County seat: Beaumont.
23. One of 39 counties in Washington, United States. County seat: Port Townsend.
24. One of 55 counties in West Virginia, United States. County seat: Charles Town.
25. One of 72 counties in Wisconsin, United States. County seat: Jefferson. Named after Jefferson County, New York.

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  Index of U.S. counties on Wikipedia.Wikipedia