Cedar Rapids is a city in Linn County, Iowa, United States, and its county seat. The population was 137,710 at the 2020 census, making it the …Cedar Rapids is a city in Linn County, Iowa, United States, and its county seat. The population was 137,710 at the 2020 census, making it the second-most populous city in Iowa. The city lies on both banks of the Cedar River, 20 miles north of Iowa City and 128 miles northeast of Des Moines, the state's capital.