SR 120 begins at an
intersection with
SR 100 (Bowdon Street) in
Tallapoosa, in Haralson County. It heads northeast into
Buchanan. Here, it first intersects
US 27 Business/
SR 1 Business. Then, it meets
US 27/
SR 1. Just before leaving the county, it enters
Draketown, where it intersects
SR 113 (Buchanan Highway). The two routes run
concurrent to the northeast. In Paulding County, it enters
Union. There, they intersect
SR 101. At this intersection, SR 113 departs to the north. About later, it intersects
SR 120 Connector (Scoggins Road). Nearly later, SR 120 enters
Dallas. Almost immediately, it meets
US 278/
SR 6 (Jimmy Campbell Parkway). At this intersection,
SR 6 Business (Buchanan Street) east begins and heads northeastward. US 278/SR 6/SR 120 head concurrently to the southeast. At the east end of town is
SR 61 (
Nathan Dean Boulevard). Farther to the east, in
Hiram, the concurrency intersects
SR 360 and Bill Carruth Parkway. At this intersection, SR 120/SR 360 head northward on Charles Hardy Parkway. Just over later, they meet SR 6 Business (Atlanta Highway). At Macland Road, SR 360 splits off to the southeast, while SR 120 continues to the northeast. A short distance later, it intersects
SR 92 (Hiram Acworth Highway). Approximately later, the road enters Cobb County. Approximately 1 Mile later, It passes through Lost Mountain Road and Eventually, Lost Mountain. Just before entering
Marietta, the highway passes through
Kennesaw Mountain National Battlefield Park. In the central part of the city, it intersects
SR 5 and the western terminus of
SR 120 Alternate (North
Marietta Parkway NW). At this intersection, SR 5/SR 120 head to the southeast. About later, they intersect SR 360 (Powder Springs Street). Only a short distance later, the two routes split. To the southeast is
Southern Polytechnic State University and then
US 41/
SR 3 (
Cobb Parkway SE). A short distance later is an
interchange with
Interstate 75 (I-75). To the northeast, the highway meets the eastern terminus of both
SR 3 Connector (Roswell Road) and SR 120 Alternate (North Marietta Parkway NE). It crosses over the
Willeo Creek into Fulton County. In
Roswell, it intersects
SR 9 (South Atlanta Street), where they begin a concurrency to the northeast. In the central part of the city, they intersect the eastern terminus of
SR 92 (East Crossville Road) and
SR 140 (Holcomb Bridge Road). For about a block, SR 140 joins the concurrency, until it departs to the northwest on Houze Road. SR 9/SR 120 pass the North Fulton Hospital, just before entering
Alpharetta. In the central part of the city, SR 9 departs to the north on South Main Street, while SR 120 heads eastward on Old Milton Parkway. Farther to the east is an interchange with
US 19/
SR 400 (Turner McDonald Parkway). In
Johns Creek, it meets
SR 141 (Medlock Bridge Road). The road crosses over the
Chattahoochee River over the Abbotts Bridge and enters Gwinnett County and the
Chattahoochee River National Recreation Area. In
Duluth is an intersection with
US 23/
SR 13 (Buford Highway). The route continues to the southeast, until just before it meets
I-85. Just before entering Lawrenceville, it meets
US 29/
SR 8 (Lawrenceville–Suwanee Road). US 29/SR 8 joins with the route shortly until meeting an interchange at exit 5 of
SR 316 (University Parkway). The city limits pass within the interchange. SR 120 continues to the southeast until it meets its eastern terminus, an intersection with
SR 20/
SR 124 in the central part of the city. ==History==