Green Grass (Lakota: wakpála phežŋ;[5] "creek [of the] grass") is a census-designated place (CDP) in Dewey County, South Dakota, United States.

[6] The community takes its name from nearby Green Grass Creek.

According to the United States Census Bureau, the CDP has a total area of 8.2 square miles (21 km2), all land.

The racial makeup of the CDP was 0.00% White, 96.55% Native American, and 3.45% from two or more races.

13.3% of all households were made up of individuals, and 6.7% had someone living alone who was 65 years of age or older.