According to a recent article in the Seattle Times the present record for most birds seen in Washington State is held by Gene Hunn at 442 out of 505 species known in the state. There are thousands of birdwatchers in the state, but only a relative handful keep serious bird lists. Living up to the excitement in the recent film "The Big Year," bird listing exists for Washington State too.
The record stands at 359th avian species witnessed in the state in 2001 by Marv Breece, of Seattle, and the record is still holding up.
Check out the article for more details.