|— City —|
|Named||"Union" in 1816|
|Incorporated||1982 (as city)|
|• Mayor||Michael O'Callaghan|
|• Total||7.13 sq mi (18.47 km2)|
|• Land||7.05 sq mi (18.26 km2)|
|• Water||0.08 sq mi (0.21 km2)|
|Elevation||922 ft (281 m)|
|• Estimate (2011)||6,448|
|• Density||910.5/sq mi (351.5/km2)|
|Time zone||EST (UTC-5)|
|• Summer (DST)||EDT (UTC-4)|
|GNIS feature ID||1049256|
Union is located at (39.900154, -84.313494).
According to the United States Census Bureau, the city has a total area of 7.13 square miles (18.47 km2), of which, 7.05 square miles (18.26 km2) is land and 0.08 square miles (0.21 km2) is water. The Stillwater River runs on its east side.
One major state highway, State Route 48, runs north and south through Union. In Union, State Route 48 is known as Main Street.
Other notable streets in Union include Martindale Road, Sweet Potato Ridge Road, and Phillipsburg-Union Road.
The city of Union, Ohio, is sometimes confused with West Union which is the county seat of Adams County, actually lies about 88 miles southeast of Union. The city of Union, Ohio, is also sometimes confused with Union City, Ohio which is northwest of Union, Oh and borders Union City, Indiana.
On November 18, 2006 Mayor Robert Packard died after collapsing while performing a wedding at city hall. Due to the city's charter the Vice-mayor (Larry Beyer) became the new mayor of Union.
 2010 census
As of the census of 2010, there were 6,419 people, 2,554 households, and 1,811 families residing in the city. The population density was 910.5 inhabitants per square mile (351.5 /km2). There were 2,721 housing units at an average density of 386.0 per square mile (149.0 /km2). The racial makeup of the city was 93.5% White, 3.6% African American, 0.2% Native American, 0.7% Asian, 0.2% from other races, and 1.8% from two or more races. Hispanic or Latino of any race were 1.6% of the population.
There were 2,554 households out of which 35.0% had children under the age of 18 living with them, 54.9% were married couples living together, 12.0% had a female householder with no husband present, 4.0% had a male householder with no wife present, and 29.1% were non-families. 24.3% of all households were made up of individuals and 9.2% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 2.99.
The median age in the city was 38.6 years. 25.5% of residents were under the age of 18; 6.8% were between the ages of 18 and 24; 26.8% were from 25 to 44; 28.1% were from 45 to 64; and 12.8% were 65 years of age or older. The gender makeup of the city was 48.1% male and 51.9% female.
 2000 census
As of the census of 2000, there were 5,574 people, 2,080 households, and 1,609 families residing in the city. The population density was 1,302.0 people per square mile (502.8/km²). There were 2,167 housing units at an average density of 506.2 per square mile (195.5/km²). The racial makeup of the city was 96.88% White, 0.91% African American, 0.14% Native American, 0.36% Asian, 0.02% Pacific Islander, 0.36% from other races, and 1.33% from two or more races. Hispanic or Latino of any race were 1.18% of the population.
There were 2,080 households out of which 40.1% had children under the age of 18 living with them, 61.1% were married couples living together, 11.8% had a female householder with no husband present, and 22.6% were non-families. 18.9% of all households were made up of individuals and 5.6% had someone living alone who was 65 years of age or older. The average household size was 2.68 and the average family size was 3.05.
In the city the population was spread out with 28.7% under the age of 18, 7.6% from 18 to 24, 33.2% from 25 to 44, 22.6% from 45 to 64, and 7.9% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 92.9 males. For every 100 females age 18 and over, there were 91.6 males.
The median income for a household in the city was $50,471, and the median income for a family was $55,139. Males had a median income of $39,944 versus $25,430 for females. The per capita income for the city was $21,260. About 2.5% of families and 3.7% of the population were below the poverty line, including 3.5% of those under age 18 and 3.5% of those age 65 or over.
Union residents west of the Stillwater River are served by the Northmont City School District of Montgomery County. The schools that Union children attend include:
- Northmont High School
- Northmont Middle School
- O. R. Edgington Elementary
- Union Elementary
East of the Stillwater River, students attend Vandalia-Butler City School District.
- http://www.union.oh.us/hist.html City history. Retrieved 16 November 2006.
- http://www.tcnewsnet.com/main.asp?SectionID=13&SubSectionID=230&ArticleID=142476&TM=238 Union's New Mayor. Retrieved December 14, 2006
- "US Gazetteer files 2010". United States Census Bureau. Retrieved 2013-01-06.
- "American FactFinder". United States Census Bureau. Retrieved 2013-01-06.
- "Population Estimates". United States Census Bureau. Retrieved 2013-01-06.
- "American FactFinder". United States Census Bureau. Retrieved 2008-01-31.
- "US Board on Geographic Names". United States Geological Survey. 2007-10-25. Retrieved 2008-01-31.
- "American FactFinder2". Retrieved 2010-03-20.
- "US Gazetteer files: 2010, 2000, and 1990". United States Census Bureau. 2011-02-12. Retrieved 2011-04-23.
- http://www.daytondailynews.com/r/content/oh/story/news/local/2007/11/08/ddn110807union. Form of Government. Retrieved 14 December 2006.
- http://www.union.oh.us/genad.html WELCOME. Retrieved 16 November 2006.
- http://www.union.oh.us/school.html Local Schools. Retrieved 16 November 2006.