Kansas Territory's western reaches encompassed the mining centers of Aurora and Pike's Peak.
Arapahoe County was proclaimed August 25, 1855 but never organized; it reverted to unorganized territory when Kansas joined the Union on January 29, 1861.
Like Arapahoe and its daughter counties, it reverted to unorganized territory upon Kansas achieving statehood.
On November 28, 1859, the Provisional General Assembly of the extralegal Territory of Jefferson established 12 counties: Although it was never officially recognized by the federal government embroiled in the debate over slavery, the provisional government of the Territory of Jefferson held effective control of what became Colorado for a year and a half.
Although the act establishing the Colorado Territory became law on February 28, 1861, the first Federal governor, William Gilpin, did not arrive in Denver until late May, and the Jefferson government disbanded itself on June 6, 1861.
The United States Census Bureau and the Office of Management and Budget currently consider the District of Columbia to consist of a single county equivalent.
In its retrospective decennial population counts the Ninth Census lists four for 1840 back to 1810, Alexandria and Washington counties alone for 1800, and none for 1790 prior to the creation of the district.
Because Kentucky began as a political dependency of Virginia, its earliest counties were organized by that government.
The following counties of Massachusetts were organized by the 1780 constitution into the District of Maine, which became a state in 1820: Other counties organized by the Illinois Territory between 1809 and 1819, including Madison, Crawford, Bond, and Edwards, notionally included parts of the future Michigan and Wisconsin territories in their boundaries, but do not appear to have exercised jurisdiction north of the current state line.
Seven counties were established by the State of North Carolina in its western territories following independence; the entire overmountain area (the former Washington District), was transferred to Federal jurisdiction in 1790 and formed into the Territory South of the River Ohio.
In 1849 most Great Basin settlers asked for admission to the Union as the State of Deseret.