Linn is a city in Washington County, Kansas, United States. As of the 2020 census, the population of the city was 387. Linn was founded in 1877…Linn is a city in Washington County, Kansas, United States. As of the 2020 census, the population of the city was 387. Linn was founded in 1877. It was named for Lewis F. Linn, a U.S. Senator from Missouri.