The present-day Union County was part of the Elizabethtown Tract, and it was purchased in 1664. The purchasers were English colonists and they bought it from the Lenape Native Americans who lived in the area of present-day Elizabeth, New Jersey. Union County was founded on March 19, 1857. Union County was the last of New Jersey's 21 counties to be established.
Many interesting historic places and neat structures can be found in the county, including on the National Register of Historic Places listings in Union County, New Jersey.
During the fall, Union County has a annual "Four Centuries in a Weekend" festival that is public, celebrating and touring historic buildings, museums and sites in the county.