city, seat (1844) of Mahaska county, southeastern Iowa, U.S. It lies between the Des Moines (Des Moines River) and South Skunk (Skunk River) rivers, about 60 miles (100 km) southeast of Des Moines. The region was inhabited by Sauk and Fox peoples when a fort was founded there by Captain Nathan Boone, nephew of Daniel Boone (Boone, Daniel), who explored the area in 1835. Settled by Quakers in 1843, it takes its name (meaning “the last of the beautiful”) from a wife of the Seminole chief Osceola. Iowa's first coal was mined near there by Welsh miners in 1870; as the mines were depleted, the city gradually became an agricultural-trade centre.

Manufacturing is mainly farm-based. Oskaloosa is the seat of William Penn College (1873), and Vennard College (1910) is at adjacent University Park. The Nelson Pioneer Farm and Craft Museum, centring on a family farm established in the 1850s, is a national historic site. Lake Keomah State Park is just east, and Lake Red Rock, a large reservoir that includes Elk Rock State Park, is about 20 miles (32 km) to the west. Inc. 1853. Pop. (1990) 10,632; (2000) 10,938.