Rio Grande City is a city in and the county seat of Starr County, Texas, United States. The population was 15,317 at the time of the 2020 cen…Rio Grande City is a city in and the county seat of Starr County, Texas, United States. The population was 15,317 at the time of the 2020 census. The city is 41 miles west of McAllen. It is connected to Camargo, Tamaulipas, via the Rio Grande City–Camargo International Bridge.