The shooting took place near McChord Air Force base in Tacoma, around 35 miles south of Seattle.
According to Pierce County Sheriff's Office spokesman Ed Troyer, the officers were sitting in a coffee shop before their shift started when a gunman entered and started shooting.
Troyer said, "We have somebody out there who blatantly went in and opened fire on four police officers, killing all four of them."
Troyer did not disclose any information about the identities of the deceased.
He only said that the officers had worked in law enforcement in Washington state for their entire careers.