Oskaloosa is a city in, and the county seat of, Mahaska County, Iowa, United States. In the late nineteenth and early twentieth century, Oskaloosa was a national center of bituminous coal mining. The population was 11,558 in the 2020 U.S. census.

The Des Moines River is a tributary of the Mississippi River in the upper Midwestern United States that is approximately 525 miles (845 km) long from its farther headwaters. The largest river flowing across the state of Iowa, it rises in southern Minnesota and flows across Iowa from northwest to southeast, passing from the glaciated plains into the unglaciated hills near the capital city of Des Moines, named after the river, in the center of the state. The river continues to flow in a southeastern direction away from Des Moines, later flowing directly into the Mississippi River.