Union is a home-rule-class city in Boone County, Kentucky, United States.

[4] According to the United States Census Bureau, the city has a total area of 3.2 square miles (8.3 km2), all of it land.

Some nearby communities, including Triple Crown Country Club, Cool Springs and Brigadoon, have Union addresses but are not part of the incorporated city and are in unincorporated Boone County.

85.3% were married couples living together, 5.1% had a female householder with no husband present, and 7.8% were non-families.

Law enforcement in the city is performed by the Boone County Sheriff's Office, which employs nearly 200 sworn deputies and 80 deputies assigned to Patrol and Traffic Divisions and is led by Sheriff Michael A Helmig.

[10] On July 8, 2022, Union Mayor Larry Solomon was joined by Boone County Judge-Executive Gary Moore and officials from Cincinnati Children's Hospital to break ground on Union Promenade, a $150 million Live/Work/Place concept co-developed by T.J. Ackermann of Thomas J. Ackermann Company, Inc., and Ralph Meierjohan of Meierjohan Building Group.

Concurrent Interstates 71/75 connect the city directly to Cincinnati (northbound) and Lexington/Louisville (southbound).