[5] According to the United States Census Bureau, the city has a total area of 19 square miles (49 km2), all land with no bay frontage.

Costanoans ("coastal peoples") were the first inhabitants, living along Alameda and Dry Creeks.

Shell mounds along the sloughs of Alameda Creek near the Alvarado sugar mill contained burial sites.

[15] Union City is a former railroad and steel town with an extensive industrial heritage.

In the 1950s, Alvarado and Decoto – the latter making up the eastern side of the town – were annexation targets of the nearby communities of Newark, Hayward, and what would become Fremont.

[17] Union City is the location of the American Licorice Company's West Coast operations, which moved there in 1971.

Union City hosts industrial and shipping companies, including R&S Manufacturing, RCD Concrete, Jatco, and EntirelyPets.

In addition, James Logan houses a 3,000-seat gymnasium and a 4,000 seat football stadium with lights.

An arts center and new track and field are available at James Logan High School.

The latter started in 1974 and runs 6 bus lines throughout Union City and parts of Hayward.

[31] Union City is served by a network of high-capacity streets, with four exits on Interstate 880 (Nimitz Freeway).

As of December 2024 the elected officials were: Gary Singh mayor,Lance Nishihira Jaime Patiño, Jeff Wang, and Scott Sakakihara.

[32] The monthly East Bay Echo[33] and bi-weekly Tri-City Voice newspapers offer local news.

[35]: 78 Bay Area Flight 93 Memorial is in Sugar Mill Landing Park.

[4] Masonic Home at Union City, a senior living community for Freemasons and their spouses, has as its centerpiece a large brick administration building.

[40] Interior features include a main staircase with stained glass windows, a parlor filled with antiques, and paintings of fourteen Masonic US presidents.

Ten more buildings were built on this 305-acre (1.2 km2) campus,[42] including Acacia Creek, a continuing care retirement community for all seniors, both Masons and non-Masons, completed in 2010.