According to the post, the woman told authorities a man was driving an unmarked, Dodge Charger, near Waterloo Rebecca Highway and the Turner County line, on Georgia Highway 32.
She said she saw blue and red lights and pulled over. The man was dressed in dark clothing and a black ski mask, and was armed with a knife.
The woman's dog, which was riding with her, began barking, and the man turned and left.
Officials said in the post that their deputies use blue lights only, and have no black unmarked cars.
They said that if a car with dash lights attempts to pull you over, you can call 911 in Irwin County to verify it's a real cop.
The traffic units are silver and marked.
If you have any information on this case, call the Irwin County Sheriff's Office at 229-468-7459.