Oelwein is a city in Fayette County, Iowa, United States. The population was 5,920 at the time of the 2020 census, a decrease of 11.5% from the 2000 census. The largest community in Fayette County, it is located at the junction of State Highways 3 and 150.

Fayette County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 19,509. The county seat is West Union.