Champaign County is a county located in the U.S. state of Ohio. As of the 2020 census, the population was 38,714. Its county seat and largest city is Urbana. The county takes its name from the French word for "open level country". Champaign County became the 18th of 88 Ohio counties on March 1, 1805. It was formed from parts of Greene and Franklin counties by legislative action.

Urbana is a city in and the county seat of Champaign County, Ohio, United States, about 34 miles (55 km) northeast of Dayton and 41 miles (66 km) west of Columbus. The population was 11,115 at the 2020 census. It is the principal city of the Urbana micropolitan area. Urbana was laid out in 1805, and for a time in 1812 was the headquarters of the Northwestern army during the War of 1812. It is the burial place of the explorer and Indian fighter Simon Kenton. The city was home to Urbana University and Curry Normal and Industrial Institute, a school for African American students.