San Isidro is a census-designated place (CDP) in Starr County, Texas, United States.

The town is named for St. Isidore the Laborer, the patron saint of farmers.

A large Southwestern Barrel Cactus growing just east of town is said to be the largest in Texas.

[17] As of the 2020 United States census, there were 187 people, 40 households, and 28 families residing in the CDP.

Out of the total population, 57.6% of those under the age of 18 and 7.1% of those 65 and older were living below the poverty line.