Oskaloosa, IA has a population of 11,538 and is the 3,528th largest city in the United States. The population density is 1,438 per sq mi which is 2533% higher than the Iowa average and 1488% higher than the national average. The median age in Oskaloosa is 37 which is approximately 3% lower than the Iowa average of 38. In Oskaloosa, 54% of the population over 15 years of age are married, 96% speak English and 2% speak Spanish. 76% of Oskaloosa residents were born in Iowa, 20% were born out of state, 1% were born outside of the United States and 3% were foreign born.