Oskaloosa is the county seat of Mahaska County, Iowa, United States. The population was 11,463 in the 2010 census, an increase from 10,938 in the 2000 census.
Oskaloosa derives its name from Ouscaloosa who according to town lore was a Creek princess who married Seminole chief Osceola. It means "last of the beautiful." The first white settlers arrived in 1835 led by Nathan Boone, youngest son of Daniel Boone who acting on instructions from Stephen W. Kearny selected it to be the first site of Fort Des Moines on a high ridge between what Skunk River and Des Moines River. The ridge was originally called the Narrows.
The town was formally platted in 1844 when William Canfield who had a trading post on the Des Moines River moved it to Oskaloosa. It became the county seat in the same year.