Lamar is the home rule municipality that is the county seat and the most populous municipality of Prowers County, Colorado. The city population was 7,687 at the 2020 United States Census. The city was named after Lucius Quintus Cincinnatus Lamar, a Confederate soldier and diplomat who wrote the Mississippi Secession Ordinance, and after the Civil War, went on to serve as U.S. Secretary of the Interior and U.S. Supreme Court Justice.