Formed February 25, 1925 (56th county)
Petroleum County (496), Winnett (186)
The 1917 stone building was converted to the courthouse in 1930. Walter Winnett designed the building. The county was established on February 25, 1925 as the 56th and last county. Winnett has always been the county seat. Petroleum County is named for local oil fields. The county seat is named for local rancher Walter John Winnett. The courthouse is on Main Street at Ashley Avenue. Montana State Highway 200 is eight blocks to the north. Walter Winnett provided the Federalist designs of this building built originally as a commercial building.
Petroleum County government consists of a sheriff and 3 Commissioners. One District Court Judge serves Petroleum, Fergus, and Judith Basin counties. Petroleum County is in central Montana. Billings, Montana is south and Great Falls, Montana is northwest of the county. The Missouri River forms its northern border. The county center is 13.9 miles North of Winnett. The county is surrounded clockwise by Phillips, Garfield, Rosebud, Musselshell, and Fergus counties.
The area of the county is 1654 square miles. It is 43 out of 56 in the state. It ranks 56 out of 56 in population in the state. It has a density of 0.3 persons per square mile making it 55 out of 56 in the state. Petroleum County has 37.5% of its population in its incorporated areas. United States Highway 87 clips its southwest border coming from the west, Fergus County, and going south, Musselshell County. The county is shaped like a highchair. Winnett is located in the southwest quarter of the county. Winnett is the county seat and, as the only incorporated city, it is the largest city. It is 37.5% of the county population. The county seat is pronounced WIN-NIT.
Winnett
