Sinai (/ˈsaɪniaɪ/ SY-nee-eye)[6] is a town in Brookings County, South Dakota, United States.

According to the United States Census Bureau, the town has a total area of 0.37 square miles (0.96 km2), all land.

There were 61 housing units at an average density of 164.9 per square mile (63.7/km2).

38.5% of all households were made up of individuals, and 9.6% had someone living alone who was 65 years of age or older.

18.5% of all households were made up of individuals, and 13.0% had someone living alone who was 65 years of age or older.

There were 4.3% of families and 5.7% of the population living below the poverty line, including 5.7% of under eighteens and none of those over 64.