Dutton, 42, was booked into the Snohomish County Jail in Everett Thursday afternoon for investigation of fourth-degree assault.
Jail records show no bail was set; Dutton is expected to appear in Snohomish County Superior Court Friday morning.
Snohomish County deputies responded to a domestic violence call at 8 a.m. Thursday and Dutton was arrested at 10 a.m. for assaulting a male relative, Sheriff's spokeswoman Shari Ireton said.
Reardon announced in February that he is resigning from his post at the end of May following months of controversy over an alleged affair with Dutton and use of staff for inappropriate activities.
Reardon was elected to a third term in 2011.
He said he made the decision to resign due to the "emotional and financial toll these relentless attacks have taken on my wife, my family and me."
During his term as the county's top executive official, Reardon was accused of using taxpayer's money for out-of-town trysts with a Dutton who said she was his mistress, off and on, for the last six years.
A Washington State Patrol investigation into those accusations produced a 13,000-page investigative report that ultimately found only one questionable charge - an unaccounted $6 cab fare.
Reardon's attorney said his client "acknowledged a lapse in judgment in his association with Ms. Dutton." The statement went on to say "her efforts to use the media to level false accusations ... needs to stop."
Dutton said she believed the Patrol investigation didn't go far enough.
Reardon also was the target of two recall petitions that were ultimately were dismissed by the courts.