Police say a heavy-set white man, believed to be in his 50s and bald posed as a contractor at a home on the 100 block of Columbine Drive in West Grove.
A woman in her early 20s let the man into the house, believing he was there to finish recent repairs.
That's when police say he attacked her, knocking her unconscious then sexually assaulting her.
A relative who was on the phone with the victim at the time heard her screams and called police.
The suspect was last seen wearing khaki pants and a light blue shirt with the name "Jeff" embroidered on it.
Anyone with information should call police.