The following are quotes from The Standard Catalog of Farm Tractors, 1890-1960 by C.H. Wendel.
"The Co-op tractor line owed its design to Dent Parrett; he had formerly been with the Parrett Tractor Company at Chicago. The original Parrett design went all the way back to 1913. Parrett continued his tractor design work after the company folded about 1922. Co-op No. 3 tractors for 1938 were built with a six-cylinder Chrysler Industrial engine using a 3 3/8 x 4 1/2 inch bore and stroke. Weighing 5,000 pounds, this tractor featured electric starting and lighting. The Co-op tractors were also capable of road speeds up to 25 mph."
"Duplex machinery Company at Battle Creek, Michigan sent a Co-op tractor to Nebraska's Tractor Test Laboratory in 1936 (Test # 275). A year or so later the name changed to the Co-operative Machinery Company and in 1940 the trade directories listed that firm as the manufacturer of the Co-op No. 2 and Co-op No. 3 tractor. Shortly afterward, World War Two began, and that all but ended the Co-op tractor line."
"With various companies involved, the history of the Co-op tractor is difficult to untangle."