Petroleum County, Montana

Petroleum County, Montana
Petroleum County Courthouse in Winnett
Location in the U.S. state of Montana
Montana's location in the U.S.
Founded	February 25, 1925
Named for	Petroleum fields
Seat	Winnett
Largest town	Winnett
Area
• Total	1,674 sq mi (4,336 km2)
• Land	1,655 sq mi (4,286 km2)
• Water	19 sq mi (49 km2), 1.1%
Population (est.)
• (2015)	475
• Density	0.3/sq mi (0/km²)
Congressional district	At-large
Time zone	Mountain: UTC-7/-6
Website	petroleumcountymt.org

Petroleum County is a county located in the U.S. state of Montana. As of the 2010 census, the population was 494, making it the least populous county in Montana and the seventh-least populous in the United States. Its county seat is Winnett. The Montana Legislature approved the formation of the county by separating it from Fergus County; Petroleum County was thus created on February 25, 1925, as the last of Montana's 56 counties.

The area was home to Native American hunter gatherer tribes of the Crow, Blackfoot, Nez Perce, and Sioux. In 1868, a trading post was established at the mouth of this river and was named Musselshell. The county seat, Winnett,was named for Walter John Winnett. He was a Canadian rancher who was captured by Sioux and later adopted into the tribe; he was given the name Eagle Eyes because of his remarkable shooting skills. Winnett established a ranch in Montana Territory in 1879 near an active trading post and the Hangman's Tree used by vigilantes in the area. The massive ranch house, which he built in 1900, housed his own family and served as a gathering place for the community. Winnett built up a freight line business to haul supplies from Billings. In 1910, he built a store and petitioned for a post office—and with that, Winnett became an official town. Fort Magginis was built in 1880 and thereafter, live stock farming proliferated. At that time, gold was also found in Fergus County, which was the original county from which Petroleum County was carved out. During the period from 1911 to 1915, stakes in the county were claimed by an influx of settlers with claims limited to 320 acres (130 ha) of land to each settler and squatter. However, in 1930 many of these lands reverted to the Government as settlers deserted the town.

Oil was discovered at the Cat Creek Oil Field on February 18, 1920, at the southeast corner of the county. Petroleum found in the Cat Creek was of high grade and extraction of crude oil started soon. In 1922, the crude oil extracted was 2.2 million barrels.