Union Valley is located approximately 5 miles (8 km) west of Quinlan in southwestern Hunt County.

Moves to incorporate Union Valley arose in response to the rapidly growing and expanding communities to the west in neighboring Rockwall County, particularly Royse City, which grew from a population of 2,957 in 2000 to approximately 9,300 in 2007.

Fears of higher taxes and a loss of the area's rural, close-knit feel were the main concerns raised by Union Valley residents.

[8] After this defeat, a series of public meetings on the issue occurred in 2007 and a second incorporation vote was held on November 6, 2007, in which it was approved by 83.3% of the voters.

Union Valley is a Class C municipality, which under state law means that the city cannot annex land totaling more than 2 square miles (5.2 km2).

[3] The Hunt County Sheriff's Department provides police services to Union Valley, as it did prior to incorporation.

[13] In addition to the incorporation vote on November 6, 2007, residents were given the option of choosing their city officials in case the proposition passed.

A non-binding referendum regarding the future imposition of a small property tax to expand the fire station was supported by the same 19–5 margin.

[16] After six months as mayor, Jay Atkins decided not to pursue another term and started his campaign for Hunt County Commissioner Precinct #2.

In municipal elections on May 10, 2008, City Secretary Eddie "Chris" Elliott was the sole candidate for mayor and received 21 votes.

In May 2010 elections were held and Mayor Eddie "Chris" Elliott ran for a second term and his opponent was Pat Miller.