Onida is a city in and the county seat of Sully County, South Dakota, United States. The population was 658 as of the 2010 census.
Onida was founded in 1880 by settlers from Oneida, New York. It received its city rights in 1883.
Onida is located at 44°42′21″N 100°4′1″W (44.705939, -100.066851).
According to the United States Census Bureau, the city has a total area of 0.64 square miles (1.66 km2), all of it land.
Onida has been assigned the ZIP code 57564 and the FIPS place code 47180.
As of the census of 2010, there were 658 people, 280 households, and 186 families residing in the city. The population density was 1,028.1 inhabitants per square mile (397.0/km2). There were 331 housing units at an average density of 517.2 per square mile (199.7/km2). The racial makeup of the city was 95.4% White, 1.8% Native American, and 2.7% from two or more races. Hispanic or Latino people of any race were 0.8% of the population.
There were 280 households of which 33.9% had children under the age of 18 living with them, 57.1% were married couples living together, 6.1% had a female householder with no husband present, 3.2% had a male householder with no wife present, and 33.6% were non-families. 30.4% of all households were made up of individuals and 9.6% had someone living alone who was 65 years of age or older.