Major Stephen H. Long made an expedition to the area now known as Weld County in 1821. He reportedly said that the region would never be fit for human habitation and should remain forever the unmolested haunt of the native hunter, bison and jackal. In 1835, a government expedition came through the general area; the next year a member of that party, Lt. Lancaster Lupton, returned to establish a trading post located just north of the present town of Fort Lupton. In about 1837, Colonel Ceran St. Vrain established Fort St. Vrain; Fort Vasquez was built south of Platteville about 1840. The latter was rebuilt in the 1930's by the State
The U.S. Congress took parts of the Territories of Nebraska, Kansas, New Mexico and Utah to create the Territory of Colorado in 1861. All parts of Colorado lying
east of Larimer County and north of the present Adams County were in the original Weld County, one of 17 counties established by the first territorial legislature in September, 1861. Weld County was named for Lewis Ledyard Weld, the first territorial secretary; St. Vrain became the first county seat.
During the first 16 years of Weld County's history the county seat was moved from St. Vrain to Latham (three miles east of the present Greeley) to Evans, to Greeley, to Evans again, and finally in 1877, returned to Greeley.
A large segment of the Weld County region was settled by people of German descent who migrated from Russia in the early 1900's. Originally they came as railroad workers; many soon worked in the productive beet fields and eventually became prosperous landowners. Weld County's Spanish-surname population began to arrive during the mid 1920's as laborers for the sugar beet industry.
Weld County's sugar beet industry began with the building of sugar factories in Greeley and Eaton in 1902. In 1903 another was built in Windsor, followed in 1920 by one at Fort Lupton and another at Johnstown in 1926.
Weld County covers an area of 3,999 square miles in north central Colorado. It is bordered on the north by Wyoming and Nebraska and on the south by the Denver metropolitan area. The third largest county in Colorado, Weld County has an area greater than that of Rhode Island, Delaware and the District of Columbia combined.
The climate is dry and generally mild with warm summers, mild winters and a growing season of approximately 138 days. The land surface is fairly level in the east, with rolling prairies and low hills near the western border. Elevations in the county range from 4,400 to 5,000 feet.
The South Platte River and its tributaries, the Cache la Poudre, Big Thompson, Little Thompson, Boulder, St. Vrain, and other smaller streams, flow into Weld County from the south and west, leaving the county on the east.