El Paso County, Kansas Territory
In July 1858, gold was discovered along the South Platte River in Arapahoe County of the Territory of Kansas (now in the State of Colorado). This discovery precipitating the Pike's Peak Gold Rush. To provide local government for the gold mining region, the Kansas Territorial Legislature split Arapahoe County into six counties on 1859-02-07: a much smaller Arapahoe County, Broderick County, El Paso County, Fremont County, Montana County, and Oro County. None of these six counties were ever organized. Many residents of the mining region felt disconnected from the territorial government, and they formed their own Territory of Jefferson on 1859-10-24.
Following the Republican Party election victories in 1860, the United States Congress admitted Kansas to the Union. The Kansas Act of Admission excluded the portion of the Kansas Territory west of the 25th meridian west from Washington from the new state, and El Paso County and the rest of this region reverted to unorganized territory.
On 1861-02-28, the Colorado Territory was organized to govern this unorganized territory and adjacent areas of the New Mexico Territory, the Utah Territory, and the Nebraska Territory. The new Colorado General Assembly organized 17 counties on 1861-11-01, including a new El Paso County for the Colorado Territory.
See also 
- El Paso County, Colorado
- Historic Colorado counties
- History of Colorado
- History of Kansas
- Pike's Peak Gold Rush
- Territory of Colorado
- Territory of Jefferson
- Territory of Kansas
- "An Act for the Admission of Kansas into the Union" (cgi-bin). Thirty-sixth United States Congress. 1861-01-29. Retrieved 2007-11-26.
- "An Act to provide a temporary Government for the Territory of Colorado" (PDF). Thirty-sixth United States Congress. 1861-02-28. Retrieved 2007-11-26.
- Colorado County Evolution by Don Stanwyck
- Kansas State Historical Society website
- Colorado State Historical Society website