Former Counties
- Ferguson County, named for Washington legislator James L. Ferguson, was established on January 23, 1863 from Walla Walla County and dissolved on January 18, 1865. Yakima County was established in its place.
- Quillehuyte County was split from Jefferson and Clallam counties in 1868 and returned to those counties a year later.
Read more about this topic: List Of Counties In Washington