Troopers said an SUV pulled onto U.S. 17 from a Shell gas station driveway off of Palemetto Bluff Road about 1:40 p.m. and into the path of the semi.
Sabrina Guthrie, 19, Roscoe Tony Kinlaw, 45, and Bo Dennis Anthony Williams Sr., 55, all of Palatka, were traveling in a Chevrolet Blazer that struck the big rig. All three died at the scene.
The FHP said the big rig swerved to the left to avoid hitting the Blazer, but the front of the tractor struck the left side of the SUV, pushing the Blazer north across the center median and into the southbound lanes.
The SUV overturned and came to rest on its roof. The FHP said none of the victims were wearing seat belts at the time of accident.
The driver of the semi was not injured. Traffic on U.S. 17 was backed up for several hours as a result of the accident.