Harlingen is a city in Cameron County in the central region of the Rio Grande Valley of the southern part of the U.S. state of Texas, about 30 miles from the coast of the Gulf of Mexico. The city covers more than 40 square miles and is the second largest city in Cameron County, as well as the fourth largest in the Rio Grande Valley. As of the 2010 census the city had a population of 64,849, for a growth rate of 12.5% since the 2000 census. It is the city with the least expensive cost of living in the United States.Harlingen is a principal city of the Brownsville–Harlingen metropolitan area, which is part of the larger Brownsville-Harlingen-Raymondville combined statistical area, included in the Matamoros–Brownsville metropolitan area.