Rancho Viejo is a town in Cameron County, Texas. The population was 2,437 at the 2010 census. The town is named from a ranch in that area named “Rancho Viejo” (Old Ranch). This ranch was owned by Blas María de la Garza Falcón, whose name was given to a nearby dam, Falcon Dam.

The median income for a household in the town was $64,038, and the median income for a family was $73,036. Males had a median income of $61,648 versus $34,750 for females. The per capita income for the town was $34,663. About 6.7% of families and 9.7% of the population were below the poverty line, including 9.9% of those under age 18 and 7.1% of those age 65 or over.