Yakima County is the second most extensive county in the U.S. state of Washington. It is named after the Yakama tribe of Native Americans. In the 2010 census, its population was 243,231. The county seat is Yakima, which is also its largest city.
The Yakama Indian Reservation, the 15th largest reservation in America, covers 1,573 mi² (4,074 km²), comprising 36% of the county's total area. Its population was 31,799 in 2000, and its largest city is Toppenish.
Yakima County was formed out of Ferguson County on January 21, 1865. Ferguson County, no longer in existence, had been created from Walla Walla County on January 23, 1863.