McPeak was taken into custody at about 10 p.m.
Hours before, the woman was taken to Meritus Medical Center with life-threatening injuries after she was taken from her home with a gunshot wound to the head, Mullendore said.
She continued to be treated for her life-threatening injuries early Saturday, the Sheriff’s Office said.
Mullendore said Friday that the man was once the victim’s boyfriend, but provided no further details about what provoked the incident.
The victim’s mother also lived at the home, but was not there during the incident, which started at 3 p.m. with a call to police about possible shots being fired, Mullendore said.
There were also three dogs in the home when the standoff began, but none of them was harmed, he said.
Police assumed that the victim was shot before police called, Mullendore said Friday.
He said police got the woman from the back of the house when the man stepped outside the front door at about 7:30 p.m.
“The outcome today was as favorable as could be. Certainly, we would have liked to not had a victim shot,’’ Mullendore said.
Forensic technicians were still busy at the scene gathering evidence Friday night, he said.
What sounded like the firing of shots could be heard in the area around 7:30 p.m.
Neighbors were either evacuated or asked to take cover in basements, Mullendore said.
“The goal is always to protect those inside as well as our own,” he said.
A helicopter landed on Dual Highway near Denny’s around 9 p.m. in case others might be injured, he said.
A woman’s voice could be heard in the neighborhood late Friday speaking to the man through what sounded like a bullhorn.
During the standoff, sheriff’s deputies and Hagerstown police officers with rifles were stood behind trees for cover, and Dual Highway was lined with more than a dozen police cars.
Any residents of the area who left their houses to check on the activity were warned to go back inside or move away.
Jerry Miller, resident of a house four or five houses down on the same side of Dual Highway said he heard nothing until police began to arrive.
“I was taking a nap in my basement,” he said. “I came outside to move my truck out from under the tree here because I heard thunder, and I saw all the cop cars.”
The Washington County Sheriff’s Office was assisted by Hagerstown police, Maryland State Police and the Special Response Team, as well as the Frederick County Special Response Team.