SR 42 begins at an
intersection with
SR 49/
SR 540 (Peach Parkway) in
Byron, in Peach County. It stairsteps its way to the west and northwest, crossing into Crawford County along the way. In
Knoxville, it intersects
US 80/
SR 22 (East Crusselle Street). The three highways head
concurrent to the west, into
Roberta, where they intersect
US 341/
SR 7 (South Dugger Avenue). Here, SR 42 leaves the concurrency of US 80/SR 22 and joins the concurrency of US 341/SR 7. The three routes travel to the north-northwest into the town of
Musella, where SR 42 splits off to the north-northeast and enters Monroe County. In
Dyas is an intersection with
SR 74. The route continues to the north-northeast, through
rural areas of the county and heads toward
Forsyth. Just before entering town, it crosses over
Tobesofkee Creek. In town, it passes by Forsyth City Cemetery before it has an intersection with
US 41/
SR 18/
SR 83 (Main Street). At this intersection, SR 83 begins a very brief concurrency through parts of town. After the two routes diverge, SR 42 curves to the northwest and parallels
Interstate 75 (I-75) for less than before resuming its north-northeast routing and an
interchange with I-75. Farther along, it crosses over the
Towaliga River. A few miles later, the road enters Butts County. SR 42 passes through
Flovilla and intersects
US 23/
SR 87 just northwest of town. At this intersection, SR 87 reaches its northern terminus and US 23/SR 42 run concurrent for most of the remainder of SR 42's length. The concurrency heads northwest into
Jackson, where they head to the west for a short while. First
SR 16, and then
SR 36 join and then leave the concurrency. US 23/SR 42 resume their north-northwest routing, passing Sylvan Grove Hospital before leaving town. They curve to the west again, traveling through the town of
Jenkinsburg, then enter Henry County. The two routes curve again to the north-northwest and pass through
Locust Grove. Then, they enter
McDonough, where they intersect
SR 155 (North McDonough Road) and then
SR 20/
SR 81. They pass by Alexander Park before crossing over Camp Creek and leaving town. Then, US 23/SR 42 enter
Stockbridge. There, they pass Eagle's Landing Parkway and then head west-northwest on a concurrency with
SR 138. The three routes curve to the northwest and reach the end of the concurrency. US 23/SR 42 resume their north-northwest routing and enter Clayton County. The two routes have an interchange with
I-675 and then travel through the town of
Rex. They skirt along the eastern edge of
Fort Gillem and pass by Conley Park, just before entering DeKalb County. US 23/SR 42 meet the northern terminus of
SR 54 Conn. (Thurman Road) before an interchange with
I-285. They pass to the east of the Lake Charlotte Nature Preserve. After that, they cross over the
South River, enter
Atlanta, and run along the
Fulton–DeKalb county line. They pass by Chestnut Hill Cemetery and meet the eastern terminus of
SR 42 Spur (McDonough Boulevard SE). Then, they pass by the western side of Brownwood Park before meeting the western terminus of
SR 260 (Glenwood Avenue SE). Just over later is an interchange with
I-20. Immediately north of there is
SR 154 (
Memorial Drive). The two highways travel through the
Little Five Points district of the city. They travel through a portion of
Freedom Park and meet the eastern terminus of
SR 42 Conn. (
Freedom Parkway). Just over later, they intersect
US 29/
US 78/
US 278/
SR 8/
SR 10 (
Ponce de Leon Avenue). At this intersection, US 23 splits off to the east, while SR 42 continues to the north. Almost immediately afterward, it curves to the northeast, re-entering DeKalb County proper. Then, it heads fairly northward, passing between
Emory University and Herbert Taylor Park and crosses over South Peachtree Creek. It intersects
SR 236 (Lavista Road NE). Then, SR 42 turns to the left onto North Druid Hills Road NE. After an interchange with
I-85, it meets its northern terminus, an intersection with
SR 13 (
Buford Highway NE). == Major intersections ==