Peterbilt Motors Company, founded in 1939, is an American manufacturer of medium- and heavy-duty Class 5 through Class 8 trucks headquartered in Denton, Texas. Peterbilt operates manufacturing facilities in Denton, Texas (1980), and Sainte-Thérèse, Quebec. From the early 1960s until the mid-1980s, the company was based in the San Francisco Bay Area of Northern California, with its headquarters, and main plant all in Newark, California. The Newark plant closed in 1980 and consolidated manufacturing at its facilities in Denton, TX and Madison, TN. In 1980 headquarters and engineering also moved to Denton. The Nashville plant was closed in 2009.