The SUV was traveling northbound and appears to have veered into the path of the 18-wheeler, which was headed southbound, according to Hunt County Sheriff Randy Meeks.
A man, woman and an infant in the SUV were killed. There was no one else in that vehicle.
DPS is investigating the cause of the crash, which took place around 1:30 p.m.
The roadway is closed in both directions and is expected to be for some time.