Agar (/ˈeɪɡɑːr/; AY-gar)[7] is a small town in Sully County, South Dakota, United States.

[9] According to the United States Census Bureau, the town has a total area of 0.16 square miles (0.41 km2), all land.

There were 48 housing units at an average density of 300.0 per square mile (115.8/km2).

47.7% of all households were made up of individuals, and 22.7% had someone living alone who was 65 years of age or older.

39.0% of all households were made up of individuals, and 19.5% had someone living alone who was 65 years of age or older.

There were no families and 7.1% of the population living below the poverty line, including no under eighteens and 6.9% of those over 64.