janb's assessment is spot on. Remember, ID has a state income tax whereas WA does not. State governments need to raise revenue to operate, hence WA does so via property tax and sales tax. WA state is also currently experiencing a huge budget deficit, so their tax structure may increase further to compensate???
When you're visiting next month, compare property taxes for similar homes in WA and ID. You may find it helpful-
Be prepared for more snow and cold in the winter than what you currently get in KY-
Good Luck!