To register to vote in Washington you must be 18 or over by the next election and a citizen of the United States.
You may register to vote online if you have a Washington driver's license or state identification card. Whether registering online or by mail your registration application must be postmarked 29 days before Election Day.
You can also register in person at your county elections office up to eight days before Election Day. If you are already registered in Washington and are moving within the state, you must update your registration by the 29th day before the election, otherwise your ballot will be sent to your previous registration address.