- 1 Berkeley Heights
- 2 Central Union County — including Cranford, Garwood,Kenilworth, Mountainside, Roselle, Roselle Park, and Westfield
- 3 Clark — home of the Dr. Wm. Robinson Plantation Museum
- 4 Elizabeth — a charming city with tree-lined streets with pretty houses
- 5 Hillside
- 6 Linden — has a large Polish-American community
- 7 Rahway
- 8 Scotch Plains — including Fanwood and Plainfield
- 9 Springfield
- 10 Summit — its downtown is on the National Register of Historic Places; including New Providence
- 11 Union (township) — home to several historic sites from the American Revolutionary War
- 12 Winfield
All of present-day Union County was part of the Elizabethtown Tract, which was purchased in 1664, by English colonists from the Lenape Native Americans that lived in the area of present-day Elizabeth, New Jersey. Union County was formed in 1857, from portions of Essex County; it was the last of New Jersey's 21 counties to be established.
Many historic places and structures are to be found in the county, including on the National Register of Historic Places listings in Union County, New Jersey.
Much of Union County is relatively flat and low-lying. Only in the northwestern corner does any significant relief appear as the Watchung Mountains cross the county. It is there that highest elevations, two areas approximately 560 feet (170 m) above sea level, are found in Berkeley Heights.
Major highways which traverse the county include the New Jersey Turnpike (I-95), the Garden State Parkway, I-78, I-278, Route 1/9, Route 22, Route 24. Route 27, Route 28, Route 35 (only in Rahway), Route 82, Route 124, Route 439, and the Goethals Bridge.
Passenger rail service is provide by NJ Transit via the Northeast Corridor, North Jersey Coast Line, Raritan Valley Line, the Morristown Line and the Gladstone Branch.
NJ Transit provides bus service to the Port Authority Bus Terminal in Midtown Manhattan, as well as service to major cities in New Jersey and within Union County.
Newark Liberty International Airport is partly located in Elizabeth, within Union County.
The Union County Performing Arts Center, in the Rahway Arts District, offers professional productions in music and theater as well as training in the performing arts.
Tomasulo Art Gallery is in the MacKay Library at Union County College's Cranford campus.
Every fall, Union County holds its annual "Four Centuries in a Weekend" festival for the public, celebrating and touring historic buildings, museums and sites in the county.