If you live in WA but your w2 says CA in box 15 for state do you need to file a state tax return?

If you worked in California, you owe tax for wages earned in California regardless of where you live, so you'll have to file a California return. Any delayed payments such as bonuses, commissions, and residuals that you earned for work done in California are also taxable in California, even if you receive the actual payment after you have left California.

If you did not work in California, you'll have to file a return to get a refund of any taxes that were erroneously paid to California.

If you did not work in California and had no taxes withheld by California, then technically you are not required to file. But you may hear from the California FTB if you don't. It would be best to see if you can get your employer to correct your W-2. If you can't, it may be best to pre-emptively file a California 540NR showing no California income.