The shooting, which also left another person wounded, erupted in Mukilteo, which sits on the bank of the Puget Sound about 30 miles north of Seattle.
According to CNN affiliate KOMO, police described the house party as a gathering of young people.
“My granddaughter called us about 20 minutes after midnight that she was hiding; that there had been a shooting and that two of her friends were shot and she was shot at,” Susan Gemmer told KOMO. “We jumped out of bed, got dressed and got in the car as fast as we could.” The city confirmed via Twitter that police arrested the suspected gunman two hours later in Lewis County after he fled the gathering of 15 to 20 people.
Police had sealed off the neighborhood but established a meeting place for parents and relatives at a nearby church.
Mukilteo, in Snohomish County, has a population of just over 20,000.
The Saturday shooting follows a club shooting in Fort Myers, Florida, early Monday morning that left a 14- and an 18-year-old dead and at least 16 others, ages 12 to 27, wounded.