There were originally five counties in the Wyoming Territory: Laramie and Carter, established in 1867; Carbon and Albany established in 1868; and Uinta, an annexed portion of Utah and Idaho, extending from Montana (including Yellowstone Park) to the Wyoming–Utah boundary.

[1] On July 10, 1890, Wyoming was admitted to the Union with thirteen counties in it.

Ten more counties were created after statehood.

[1] Two counties were renamed after their creation.

[3] The Federal Information Processing Standard (FIPS) code, which is used by the United States government to uniquely identify states and counties, is provided with each entry.