EUCLID, Ohio — A service for a Marine killed in Iraq last week was held in his mother’s front yard, where about 60 friends and neighbors gathered to honor Sgt. Mark Smykowski.

His brothers, fellow Marines Darren and Kenny Smykowski, saluted as an American flag was raised and then lowered to half-staff during the memorial Tuesday in this Cleveland suburb.

Their 23-year-old brother was killed June 6 when a roadside bomb struck his armored Humvee. He will be buried at Arlington National Cemetery.

“This is the saddest day in my life but also the proudest,” Smykowski’s mother, Diana Ross, told the crowd gathered on her lawn. “My son’s death was not in vain. No Marines’ deaths are in vain.”

Some came to pay their respects even though they did not know Smykowski, who was assigned to 2nd Reconnaissance Battalion, 2nd Marine Division, II Marine Expeditionary Force, based in Camp...