Oskaloosa , city (1990 pop. 10,632), seat of Mahaska co., SE Iowa, on the North and South Skunk rivers; inc. 1852. It is the trade and processing center of a rich farm and livestock area. Machinery, feeds, egg products, and steel are manufactured. Coal has been mined there for over 100 years. A small fort was established there in 1835, and it became a post on a much-traveled westward trail. The city was settled (1844) by Quakers. William Penn Univ. and Vennard College are there.