The truck was transitioning from State Route 154 onto State St. when its brakes apparently failed, according to the California Highway Patrol.
The devastating crash flattened the small wooden home and buried some sections in gravel.
Investigators say a father, mother and their 7-year-old son were killed. There were fears that a fourth family member may have also been a victim, but authorities determined that nobody else was home at the time.
Coroner's officials haven't named the victims but a neighbor said they're Leo and Lorena Leon and their 7-year-old son.
The driver of the truck was treated at the scene for facial cuts.
There are strong indications the trucks brakes were not working. There is no sign of drinking or drugs were involved. The truck's brakes started being a problem after the driver picked up a load in Santa Ynez.
"He stated the he used every available brake resource that he had, his foot brakes, the hand brake, everything you could try he said he attempted," said California Highway Patrol Officer Jeremy Wayland. "Right now alcohol is not a factor in the collision. He voluntarily gave a sample of his breath and he voluntarily gave a sample of his blood."
The driver apparently tried to miss a hotel and offices but couldn't avoid cars and the cabin.
Nancy Schliemann runs the motel that rented the family the cabin. It was the fourth major truck accident she's seen at the 154/101 intersection in 12 years.
"We said at that time five or six years ago that this was going to take someone dying for something to be done about this and this family was a wonderful family, they were hard-working people and it's just an unnecessary loss of life today," said Schliemann.
The crash investigation continues.
The Associated Press contributed to this story.