Wilson County is located in the U.S. state of Kansas. As of 2000, the population was 10,332. Its county seat is Fredonia.

Allen, Anderson, Arapahoe (CO), Atchison, Breckinridge, Bourbon, Browne, Butler, Calhoun, Coffey, Davis, Doniphan, Dorn, Douglas, Franklin, Greenwood, Godfroy, Hunter, Jefferson, Johnson, Leavenworth, Linn, Lykins, Madison, Marion, Marshall, McGee, Nemaha, Richardson, Riley, Shawnee, Washington, Weller, Wilson, Wise and Woodson Counties were formed in 1855 as the original 36 counties in the Kansas Territory.

Following amendment to the Kansas Constitution in 1986, the county remained a prohibition, or "dry," county until 1998, when voters approved the sale of alcoholic liquor by the individual drink with a 30% food sales requirement.

According to the U.S. Census Bureau, the county has a total area of 575 square miles, of which, 574 square miles of it is land and 1 square mile of it (0.20%) is water.