Port Isabel is a city in Cameron County, Texas, United States. It is part of the Brownsville–Harlingen–Raymondville and the Matamoros–Brown…Port Isabel is a city in Cameron County, Texas, United States. It is part of the Brownsville–Harlingen–Raymondville and the Matamoros–Brownsville metropolitan areas. The population was 5,028 at the 2020 census.