The incident unfolded just after 10 p.m. Friday at the woman's home in the 8200 block of Union Mills Road SE.
The 23-year-old woman was at home alone when her dog started barking incessantly and wouldn't stop. When the woman opened the door to let the dog outside, she was confronted by a man with a knife.
The man forced his way into the house and sexually assaulted the woman. He then forced her to give him all her cash and the keys to her car, Thurston County sheriff's officials said.
The man drove off in the woman's car, a white Volkswagen Jetta with license plate number AFA 5251.
The suspect is described as a skinny white male standing about 5-feet-10-inches tall, wearing a dark hoodie and dark pants. His face was covered with a red bandana or handkerchief.
Sheriff's detectives are actively investigating. Anyone with information is asked to call 911.