Several historical maps of Washington are found in Ralph N. Preston, Early Washington: Overland Stage Routes, Old Military Roads, Indian Battle Grounds, Old Forts, Old Gold Mines. Corvallis, Oregon: Western Guide Publishers, 1974. (Family History Library book Q 979.7 E3e.)
United States Census Bureau State and County Map. This map will allow you to zoom in on any state or county in the United States and read the names of all of the neighboring counties.
The Family History Library has several maps of Washington. Larger collections of maps are available at the University of Washington in Seattle and Western Washington State College in Bellingham.
University of Washington in Seattle: http://www.washington.edu/
Western Washington State College in Bellingham: http://www.wwu.edu/
Printable maps are also available from the National Atlas of the United States -- http://nationalatlas.gov/printable.html