Skagit County, Washington (data.census.gov) Skagit County, Washington has 1,730.2 square miles of land area and is the 21st largest county in Washington by total area. Skagit County, Washington is bordered by Chelan County, Washington, Whatcom County, Washington, Snohomish County, Washington, Okanogan County, Washington, Island County, Washington, and San Juan County, Washington.