Marion is a city in Linn County, Iowa, United States. The population was 26,294 at the 2000 census and was 41,535 in 2020, an increase of 58%. The city is located next to Cedar Rapids and part of the Cedar Rapids Metropolitan Statistical Area. Marion was designated as the first Linn County seat before it was moved to the larger neighbor Cedar Rapids in 1919. Today, Marion is a primarily suburban community with a historic downtown center, and is one of the fastest-growing cities in Iowa.