State Route 120 begins at SR 100 near Tallapoosa

Tallapoosa, Georgia

Tallapoosa is a city in Haralson County, Georgia, United States. The population was 2,789 at the 2000 census.-Geography:Tallapoosa, incorporated in 1860, is located in Haralson County, in northwest Georgia, about west of Atlanta, just north of Interstate 20 and east of the Alabama state line...

 and ends at West Crogan Street (U.S. 29/SR 8) in Lawrenceville

Lawrenceville, Georgia

Lawrenceville is a city in and the county seat of Gwinnett County, Georgia, in the United States. The Census Bureau estimates the 2008 population at 29,258...

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In Marietta

Marietta, Georgia

Marietta is a city located in central Cobb County, Georgia, United States, and is its county seat.As of the 2010 census, the city had a total population of 56,579, making it one of metro Atlanta's largest suburbs...

, SR 120 has a spur route (SR 120 Alternate), which acts as a perimeter for the northern part city. In Paulding County

Paulding County, Georgia

Paulding County is a county located in the U.S. state of Georgia. As of the 2010 census, the population was 142,324. The county seat is Dallas....

, the highway cosigns with the following highways (SR 360

State Route 360 (Georgia)

State Route 360 is a state highway located in northwest Georgia. The route begins with its intersection with U.S. 278/S.R. 6 near Dallas and travels to the east cosigned with S.R. 120 for a short distance. The routes then diverge, with S.R. 360 routed on Macland Road. The route exits Paulding...

). Then it cosigns with (U.S. 278) through Dallas

Dallas, Georgia

Dallas is a city in and the county seat of Paulding County, Georgia, United States. As of the 2010 census, the city had a population of 11,544. It was named for George M. Dallas, Vice President of the United States of America under James K. Polk.-History:...

. In western Paulding County and eastern Haralson County

Haralson County, Georgia

Haralson County is a county located in the U.S. state of Georgia. It was created on January 26, 1856 and was named for Hugh A. Haralson. As of 2000, the population was 25,690. The 2007 Census Estimate shows a population of 28,718...

, SR 120 cosigns with (SR 113). While in northern Fulton County

Fulton County, Georgia

Fulton County is a county located in the U.S. state of Georgia. Its county seat is Atlanta, the state capital since 1868 and the principal county of the Atlanta metropolitan area...

, it cosigns with (SR 9) and (SR 140) although SR 140 just briefly cosigns the highway in Roswell

Roswell, Georgia

Roswell is a city located in northern Fulton County; it is a suburb of northern Atlanta, Georgia, United States. The 2010 Census population was 88,346. It is the eighth largest city in Georgia...

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History

From 1969 to 2007, SR 120 Loop looped around Marietta. In October 2007, SR 120 Loop was decommissioned, and mainline SR 120 was rerouted to the southern part of the loop. Prior to October 2007, mainline SR 120 ran through downtown Marietta and formed the southern part of Marietta Square. The portion of SR 120 from U.S. 41/SR 3 to SR 120 Alternate was renumbered SR 3 Connector. This was done at the same time changes were made to SR 5.