Los Fresnos is a city in Cameron County, Texas, United States. The population was 8,114 at the 2020 census, up from 5,542 at the 2010 census. It is part of the Brownsville–Harlingen–Raymondville and the Matamoros–Brownsville metropolitan areas. Located in south-central Cameron County, the city was named for the fresnos scattered in the woods and along streams.