Does the County Assessor have the right to access your property?

Yes, the County Assessor does have the right to access your property in order to make an inspection for valuation pursuant to RCW 84.40.025 which reads as follows:

RCW 84.40.025
Access to property required.

For the purpose of assessment and valuation of all taxable property in each county, any real or personal property in each county shall be subject to visitation, investigation, examination, discovery, and listing at any reasonable time by the county assessor of the county or by any employee thereof designated for this purpose by the assessor.

In any case of refusal to such access, the assessor shall request assistance from the department of revenue which may invoke the power granted by chapter 84.08 RCW.