Weld County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 328,981. The county seat is Greeley.

United Air Lines Flight 629, registration N37559 and dubbed Mainliner Denver, was a Douglas DC-6B aircraft that was blown up on November 1, 1955, by a dynamite bomb placed in the checked luggage. The explosion occurred over Longmont, Colorado, United States, at 7:03 p.m. local time, while the airplane was en route from Denver to Portland, Oregon, and Seattle, Washington. All 39 passengers and 5 crew members on board were killed in the explosion and crash.