State Route 40 (SR 40) is a 21.184-mile-long (34.092 km) state highway in the northeastern part of the U.S. state of Alabama. The western terminus of the highway is at its intersection with SR 35 near Scottsboro. The eastern terminus of the highway is at its intersection with SR 117 at Hammondville, just north of the intersection of SR 117 with Interstate 59 (I-59).

SR 40 travels across the base of Lookout Mountain. The narrow, twisty roadway continues until the highway reaches Dutton in western DeKalb County. East of Dutton, the roadway has fewer curves as it continues across the county. While SR 40 does not directly have an interchange with I-59, there is direct access to I-59 via SR 117 approximately 1 mile (1.6 km) southeast of the eastern terminus of the highway.

County	Location	mi	km	Destinations	Notes
Jackson	​	0.000	0.000	SR 35 – Section, Scottsboro	Western terminus
	​	6.936	11.162	SR 71 – Trenton, Section, Pisgah
DeKalb	Henagar	14.941	24.045	SR 75 – Trenton, Rainsville
	​	21.184	34.092	SR 117	Eastern terminus
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

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