Rock County Deputies responded to the accident at the intersection of Highway 26 & County N in the town of Milton just before 6:00 p.m. Thursday night.
Authorities say a 17-year old Madison girl driving a BMW, stopped at the stop sign but when she proceeded to cross the intersection, the semi tractor-trailer which was going northbound on Highway 26, hit the car.
The driver of the BMW was taken to the hospital and treated for minor injuries. Deputies cited her for failing to yield from a stop sign.
Three of her passengers were taken to the hospital, as well; two of the passengers suffered serious internal injuries and one is listed in Critical Condition.
The driver of the semi-tractor trailer, a 43-year old man from Canada, was not hurt.
Highway 26 was closed for approximately three and a half hours so responders could investigate and clear intersection.