Union is a village in McHenry County, Illinois, United States. The population was 580 at the 2010 census, up from 576 in 2000.
Union is located at 42°14′7″N 88°32′33″W / 42.23528°N 88.54250°W / 42.23528; -88.54250 (42.235237, -88.542379).
According to the 2010 census, Union has a total area of 0.83 square miles (2.15 km), all land.
As of the census of 2000, there were 576 people, 204 households, and 158 families residing in the village. The population density was 950.4 people per square mile (364.6/km²). There were 208 housing units at an average density of 343.2 per square mile (131.7/km²). The racial makeup of the village was 98.09% White, 0.35% Native American, 0.87% from other races, and 0.69% from two or more races. Hispanic or Latino of any race were 3.99% of the population.
There were 204 households out of which 37.7% had children under the age of 18 living with them, 63.7% were married couples living together, 9.3% had a female householder with no husband present, and 22.5% were non-families. 15.7% of all households were made up of individuals and 6.4% had someone living alone who was 65 years of age or older. The average household size was 2.82 and the average family size was 3.15.
In the village, the population was spread out with 28.0% under the age of 18, 7.5% from 18 to 24, 34.2% from 25 to 44, 19.3% from 45 to 64, and 11.1% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 92.6 males. For every 100 females age 18 and over, there were 97.6 males.
The median income for a household in the village was $56,528, and the median income for a family was $57,500. Males had a median income of $38,393 versus $25,536 for females. The per capita income for the village was $21,218. About 5.8% of families and 5.2% of the population were below the poverty line, including 2.9% of those under age 18 and 16.7% of those age 65 or over.