Weld County - A territory was created from parts of both Kansas and Nebraska Territories in 1859, named Jefferson Territory. It had 12 counties, including St. Vrain County, named in honor of the French traders, Ceran and Marcellaine St. Vrain. Weld County was founded November 1, 1861, when the Colorado General Assembly organized 17 counties in the new Colorado Territory. November 28, 1861 Colorado Territory was recognized by Congress and divided into 17 counties. St. Vrain County was renamed Weld County on September 9, 1861. The first three official post offices in Old Weld County were Fort Lupton, Julesburg and St. Vrain. Weld County was named for Lewis Ledyard Weld, a lawyer and territorial secretary. Until February 9, 1887, Weld County's boundaries included the area now compromising Weld County plus the counties of Washington, Logan, Morgan, Yuma, Phillips and Sedgwick.