[2] The county was created in 1901 and named for President William McKinley.

[3] McKinley County is Gallup's micropolitan statistical area.

According to the U.S. Census Bureau, the county has a total area of 5,455 square miles (14,130 km2), of which 5.5 sq mi (14 km2) (0.1%) are covered by water.

[4] For purposes of census-data collection, organization and analysis, the United States Census Bureau has devised 44 census-designated places since 1980 within McKinley County.

As of the 2000 census,[10] 74,798 people, 21,476 households, and 16,686 families were living in the county.

As of the 2010 census, 71,492 people, 21,968 households, and 16,219 families resided in the county.

[13] For purposes of census-data collection, organization and analysis, the United States Census Bureau has devised 44 census-designated places since 1980 within McKinley County.

[19] During its early history from 1912 to 1928, McKinley County voted for the Republican candidate in every presidential election.

From 1932 onward, the county, with its large Native American majority, has backed Democratic candidates in all but three presidential elections that were national landslides for the Republican Party.