State Route 166 (SR 166) is a state highway in the U.S. state of Georgia. It connects the Alabama state line with the city of Atlanta. The highway travels through Carrollton, McWhorter, and East Point. Except for the Carrollton and East Point/Atlanta areas, the highway is fairly rural. In Atlanta, it has a limited-access freeway portion that is known as the Arthur B. Langford Jr. Parkway.

Carroll County is a county located in the northwestern part of the State of Georgia. As of the 2020 census, its population was 119,148. Its county seat is the city of Carrollton. Carroll County is included in the Atlanta-Sandy Springs-Roswell metropolitan statistical area and is also adjacent to Alabama on its western border.