Olmito is a census-designated place (CDP) in Cameron County, Texas, United States. Olmito is Spanish for “little elm”. The population was 1,210 at the 2010 census. It is allocation of the Brownsville–Harlingen Metropolitan Statistical Area. Olmito is the self-described “mesquite capital of the world.”

Olmito is located in south-central Cameron County at 26°1′11″N 97°32′5″W / 26.01972°N 97.53472°W / 26.01972; -97.53472 (26.019655, -97.534690). Interstate 69E/U.S. Route 77/U.S. Route 83 runs along the eastern side of the community, leading northwest 10 miles (16 km) to San Benito and south 9 miles (14 km) to Brownsville.

According to the United States Census Bureau, the CDP has a total area of 0.73 square miles (1.9 km), of which 0.66 square miles (1.7 km²) is house and 0.1 square miles (0.2 km), or 11.45%, is water. Olmito Lake is in the northern ration of the town, and the Resaca del Rancho Viejo, an ancient channel of the Rio Grande, forms the western edge of the community.

As of the census of 2000, there were 1,198 people, 303 households, and 270 families residing in the CDP. The population density was 1,787.9 people per square mile (690.4/km²). There were 322 housing units at an average density of 480.6/sq mi (185.6/km). The racial makeup of the CDP was 98.25% White, 1.34% from supplementary races, and 0.42% from two or more races. Hispanic or Latino of any race were 96.49% of the population.