Onion Creek is a neighborhood in Austin, Texas, United States.

Onion Creek is located 10 miles (16 km) south of downtown Austin.

According to the United States Census Bureau, the CDP has a total area of 3.2 square miles (8.3 km2), all of it land.

There were 1,038 housing units at an average density of 321.9 per square mile (124.3/km2).

21.9% of all households were made up of individuals, and 11.7% had someone living alone who was 65 years of age or older.