|Area||0.76 sq mi (2 km2)|
|- land||0.76 sq mi (2 km2)|
|- water||0.00 sq mi (0 km2)|
|- summer (DST)||CDT (UTC-5)|
|Wikimedia Commons: Oneida, Illinois|
According to the 2010 census, Oneida has a total area of 0.76 square miles (1.97 km2), all land.
As of the census of 2000, there are 752 people, 303 households, and 226 families residing in the city. The population density is 1,035.9 inhabitants per square mile (397.7/km²). There are 308 housing units at an average density of 424.3 per square mile (162.9/km²). The racial makeup of the city is 98.27% White, 0.00% African American, 0.13% Native American, 0.66% Asian, 0.00% Pacific Islander, 0.66% from other races, and 0.27% from two or more races. 1.33% of the population are Hispanic or Latino of any race.
There are 303 households out of which 32.3% have children under the age of 18 living with them, 61.4% are married couples living together, 9.6% have a female householder with no husband present, and 25.4% are non-families. 24.1% of all households are made up of individuals and 11.9% have someone living alone who is 65 years of age or older. The average household size is 2.48 and the average family size is 2.91.
In the city, the population is spread out with 24.1% under the age of 18, 9.2% from 18 to 24, 24.6% from 25 to 44, 25.1% from 45 to 64, and 17.0% who are 65 years of age or older. The median age is 39 years. For every 100 females there are 96.9 males. For every 100 females age 18 and over, there are 89.1 males.
The median income for a household in the city is $39,712, and the median income for a family is $46,250. Males have a median income of $31,974 versus $17,969 for females. The per capita income for the city is $16,991. 5.3% of the population and 4.8% of families are below the poverty line. Out of the total population, 10.5% of those under the age of 18 and 2.2% of those 65 and older are living below the poverty line.
ROWVA School District #208 is made up of five major towns: Rio, Oneida, Wataga, Victoria, and Altona. PreK-2nd graders go to ROWVA Central in Oneida, 3rd and 4th graders attend ROWVA Central in Oneida Illinois. 5th and 6th graders go to ROWVA East in Altona. The junior high is located in Oneida and is made up of 7th and 8th graders. The high school made up of 9th-12th graders and is also located in Oneida. ROWVA Central, ROWVA Jr. High, and ROWVA High School are all in one basic building, in different sections. ROWVA's school colors are black, gold, and white, with their mascot being a tiger. The school ended a five-year-long football co-op with AlWood at the end of the 2009 football season, in which they are the A&R Bulldogs (black, silver, and white). Starting the 2009 fall season, ROWVA is also part of a sports co-op with Galva where they are the Mid-County Cougars (black, blue, and white). ROWVA is a part of the Mid-County co-op for golf, cross country, junior high football, and will be high school football starting in the 2010 football season.
- A. T. McMaster, Illinois legislator and farmer, was born in Oneida.
- Kid Mohler, second baseman for the Washington Senators, was born in Oneida.
- Donald L. Moffitt, member of the Illinois House of Representatives, served as mayor of Oneida from 1972 to 1975.
- "G001 - Geographic Identifiers - 2010 Census Summary File 1". United States Census Bureau. Retrieved 2015-12-27.
- "Population and Housing Unit Estimates". Retrieved June 9, 2017.
- "Census of Population and Housing". Census.gov. Retrieved June 4, 2015.