Ottumwa (pronounced "Uh-tuhm-wa") is a city in Wapello County, Iowa. The population was 24,998 at the 2000 census. It is the county seat of Wapello County^GR6.

It is located in the southeastern part of Iowa, and the city is split into northern and southern halves by the Des Moines River.

Ottumwa is the birthplace of Tom Arnold, the home of notorious rare book thief Stephen Blumberg, and of the fictional character Radar O'Reilly from the television program M*A*S*H. Tom Arnold and Roseanne Barr briefly owned a home together in Ottumwa before their divorce in 1994; they also owned a restaurant, the Big Food Diner, in nearby Eldon, Iowa, from 1993 through 1995. Also, future US President Richard Nixon was stationed here from October 1942 to May 1943 at the Ottumwa Naval Reserve Aviation Base where he served as Aide to the Executive Officer.