The 59-year-old man, whose name was not released, was arrested in McCleary, about 80 miles southwest of Monroe Correctional Complex, said Grays Harbor County Chief Criminal Deputy Steve Shumate.
A vehicle was seized, but neither Shumate nor corrections department spokesman Chad Lewis would say how they think the man assisted in the escape of Brandon J. Musto.
Musto, 37, had three months left to serve on his sentence when turned up missing Wednesday evening at the minimum security unit.
Prisoners are counted four times a day so he could not have been gone more than a few hours before he was missed, said Lewis.
Musto apparently went over a fence, although officials are checking video as they investigate, Lewis said.
Musto began serving time in September 2011 for a for vehicular assault conviction in Thurston County and was scheduled for release in February 2013.
Lewis said authorities do not know Musto's motive, but since an escape conviction could lead to several more years in prison, "that might be the first question we ask him."
"You have a foot out the door, there's little incentive," to escape, Lewis said.
There was nothing notable in Musto's prison record and his behavior had to be good to qualify for minimum security, Lewis said Thursday.
Minimum security is one of five units at the prison complex at Monroe, 24 miles northeast of Seattle. The unit holds about 460 of the 2,500 offenders housed in the state's second-largest prison, smaller by a few hundred inmates than the Coyote Ridge Corrections Center near the Tri-Cities.
Anyone spotting Musto is asked to call 911. He's described as white, 5-foot-8, 180 pounds with brown eyes and dark hair. He has tattoos on his right arm and left wrist.
It's been years since the last escape from the Monroe prison and Lewis couldn't recall one. Other recent problems at the facility, however, have made news.
A corrections officer was assaulted in the special offenders unit at Monroe in August and had to be treated at a Seattle hospital.
And in January 2011, Corrections Officer Jayme Biendl was strangled in the prison chapel. Inmate Byron Scherf is charged with aggravated murder and is scheduled for trial in March in Everett.