According to Arthur Wallenstein, director of Montgomery County Corrections, Arenas arrived at the Montgomery County jail at 7:40 p.m. Arenas must spend two days there for medical screening and classification before being transferred to the county's Pre-Release Center, a halfway house.
Arenas was sentenced March 26 to 30 days in a halfway house for bringing weapons into the Verizon Center. Corrections officials in Montgomery County agreed to let him serve his sentence there, as part of an agreement with the U.S. Bureau of Prisons.
Arenas pleaded guilty to a felony gun charge in January, and has been suspended until the end of the season by the NBA.
Arenas also received two years of probation, a $5,000 fine and 400 hours of community service that can't be performed at basketball clinics.
"Our thoughts are always with him. We're glad that it's going to be done, and he'll be able to move on," Washington coach Flip Saunders said after the Wizards' 106-96 victory in Boston on Friday night.
Wizards guard Shaun Livingtson also commented on Arenas.
"He is who he is for a reason," Livingston said. "He's done so much for this team. I have nothing but positive things to say about him. But all I can do is focus on me."
Andray Blatche looked forward to Arenas' return.
"Gil's going to come back next season humble," Blatche said. "We miss him and we can't wait to have him back."