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, an accumulation from 10,938 in 2000.

Oskaloosa derives its reveal from Ouscaloosa who, according to town lore, was a Creek princess who married Seminole chief Osceola. A local tradition was that her read out meant “last of the beautiful.” (This explanation of “last of the beautiful” is not correct. “Oskaloosa” in the Mvskoke-Creek language means “black rain,” from the Mvskoke words “oske” (rain) and “lvste” (black). “loosa” is an English sullying of the Mvskoke word “lvste”. See for example the Wikipedia entrance for Tuskaloosa, eponym of the town of Tuscaloosa, Alabama. In complement the Mvskoke word “Ouscaloosa” means “Black Water”).
The first European-American settlers arrived in 1835, led by Nathan Boone, youngest son of frontiersman Daniel Boone. Acting on instructions from Stephen W. Kearny, he fixed this as the first site of Fort Des Moines, located upon a high ridge amid the Skunk and Des Moines rivers. The ridge was originally called the Narrows.

The town was formally platted in 1844 subsequently William Canfield moved his trading read out from the Des Moines River to Oskaloosa. The town was designated by the legislature as the county chair in the same year.

The Des Moines Valley Railroad built north from Eddyville, Iowa through Oskaloosa to Pella, Iowa in 1864. In 1873, this became the Keokuk and Des Moines Railroad, and in 1887, it was leased by the Chicago, Rock Island and Pacific Railroad. The Central Iowa Railway followed, which became the Iowa Central Railway in 1888 and was absorbed by the Minneapolis and St. Louis Railway in 1901. In 1883, the Burlington and Western Railway reached Oskaloosa; this was a narrow gauge lineage that was widened to Standard Gauge in 1902 and later merged in the reveal of the Chicago, Burlington and Quincy Railroad.