Peterbilt Motors Company is a manufacturer of medium- and heavy-duty Class 5 through Class 8 trucks headquartered in Denton, Texas. The company is a subsidiary of PACCAR. Founded in 1939, Peterbilt operates manufacturing facilities in Madison, Tennessee (1969), 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, parts department, and main plant all in Newark, California. The Newark plant closed in 1986; headquarters moved to Denton, and engineering moved to Denton in 1993.