Lamar is a census-designated place and unincorporated community in Benton County, Mississippi, United States. It is located along Mississippi Highway 7 in western Benton County. Lamar has a post office with the ZIP code 38642. The nearly abandoned Mississippi Central Railroad runs through Lamar, and is only used rarely for freight trafficking. It was first named as a CDP in the 2020 Census which listed a population of 39.