Niantic is a village in Macon County, Illinois, United States whose population was 699 at the 2010 census.
It is included in the Decatur, Illinois Metropolitan Statistical Area.
Niantic is located at 39°51′18″N 89°09′56″W / 39.854922°N 89.165546°W / 39.854922; -89.165546.
According to the 2010 census, Niantic has a total area of 1.07 square miles (2.77 km), all land.
As of the census of 2000, there were 738 people, 269 households, and 200 families residing in the village. The population density was 686.7 people per square mile (266.3/km²). There were 299 housing units at an average density of 278.2 per square mile (107.9/km²). The racial makeup of the village was 99.59% White, 0.14% Native American, and 0.27% from two or more races. Hispanic or Latino people of any race were 0.68% of the population.
There were 269 households out of which 37.9% had children under the age of 18 living with them, 62.8% were married couples living together, 7.4% had a female householder with no husband present, and 25.3% were non-families. 21.6% of all households were made up of individuals and 9.7% had someone living alone who was 65 years of age or older. The average household size was 2.74 and the average family size was 3.18.
In the village, the population was spread out with 31.2% under the age of 18, 7.3% from 18 to 24, 28.7% from 25 to 44, 19.5% from 45 to 64, and 13.3% who were 65 years of age or older. The median age was 33 years. For every 100 females, there were 99.5 males. For every 100 females age 18 and over, there were 94.6 males.
The median income for a household in the village was $41,184, and the median income for a family was $42,500. Males had a median income of $33,750 versus $21,500 for females. The per capita income for the village was $19,448. About 5.7% of families and 7.8% of the population were below the poverty line, including 9.4% of those under age 18 and 9.2% of those age 65 or over.