Harlingen is located in Cameron County in the heart of the Rio Grande Valley of south Texas, United States, about 30 miles from the coast of the Gulf of Mexico. The city covers more than 34 square miles, and is the second largest city in Cameron County and the sixth largest in the Rio Grande Valley. As of the 2010 Census the city had a total population of 64,849 and grew 12.5% since the 2000 Census.

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.

The median income for a household in the city was $30,296, and the median income for a family was $34,015. Males had a median income of $27,014 versus $21,795 for females. The per capita income for the city was $13,886. About 19.3% of families and 24.9% of the population were below the poverty line, including 34.7% of those under age 18 and 16.2% of those age 65 or over.