Oskaloosa is a city located in Mahaska County, Iowa, United States. It is the county seat and has a population of approximately 11,500 residents as of the 2020 census. Oskaloosa is known for its historic downtown area, which features many well-preserved buildings from the 19th century. The city is also home to William Penn University, a private four-year liberal arts college. Oskaloosa offers a range of recreational activities, including parks, trails, and a lake for boating and fishing. The city hosts several annual events, such as the Southern Iowa Fair and the Sweet Corn Serenade music festival.