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) is a census-designated place (CDP) in Humboldt County, California, United States. McKinleyville is located north of Arcata, at an elevation of 141 feet (43 m). The population was 13,599 at the 2000 census. It is also the location of the Arcata-Eureka Airport.
According to the United States Census Bureau, the CDP has a total area of 22.8 square miles (59.1 km²), of which, 20.9 square miles (54.1 km²) of it is land and 1.9 square miles (5.0 km²) of it (8.42%) is water.
McKinleyville consists of several watershed areas. The north bank of the Mad River in the farthest watershed to the south. Next watershed to the north is Mill Creek, then Strawberry Creek, Widow White Creek, Norton Creek, Patrick Creek and finally the farthest watershed to the north is the south bank of the Little River. To the west lies the Pacific Ocean.