State Route 21 (SR 21) is a 279-mile (449 km) state highway that extends from the Florida state line, near Atmore in Escambia County to Piedmont in Calhoun County. The route travels almost the entire length of the state from the northeast to the southwest. It is the longest signed state route in Alabama.

Starting at the northern terminus of Florida State Road 97 at the Florida state line south of Atmore, the route travels north through Atmore, passing under an intersection with Interstate 65 at exit 57, then enters Monroe County and travels northeast through Frisco City and Monroeville and is concurrent with SR 47 for part of this section. SR 21 then once again becomes a standalone route passing through Beatrice and Oak Hill. In Lowndes County, SR 21 begins its first concurrency with US 80, and the two highways enter Montgomery, the state capital, from the southwest. SR 21 then diverges northeastward from US 80 for a short concurrency with US 31, then travels concurrently with US 80 once again (as well as US 82) around the Montgomery city center, diverging from US 82 at US 231 and traveling concurrently with US 231 northward to Sylacauga at an interchange with US 280. From Sylacauga, SR 21 turns northeastward toward Talladega. The route travels close to the Talladega National Forest and the Talladega Superspeedway. From here, SR 21 continues generally northeastward through the cities of Oxford, Anniston, and Jacksonville before terminating at an intersection with U.S. Highway 278 in Piedmont. The route is paved throughout and often multi-lane.

County	Location	mi	km	Destinations	Notes
Escambia	Atmore	0.000	0.000	SR 97 south – Pensacola	Florida state line
		1.888	3.038	US 31 (Nashville Avenue / SR 3) – Mobile, Brewton
	Freemanville	8.122	13.071	I-65 – Mobile, Montgomery	I-65 exit 57
Monroe	Uriah	22.372	36.004	SR 59 south – Stockton, Upper Delta Wildlife Management Area	Northern terminus of SR 59
	Frisco City	33.680	54.203	SR 21 Truck north (Bowden Street) / CR 18 (Wild Fork Road)
		34.080	54.846	SR 21 Truck south (Highway 21 By-Pass)
	​	38.087	61.295	US 84 / SR 41 south / SR 47 Truck south (SR 12) – Grove Hill, Evergreen, Conecuh County	Southern end of SR 41/SR 47 Truck concurrency
	Ollie	38.517	61.987	SR 136 east to I-65 north	Western terminus of SR 136
	Monroeville	40.864	65.764	SR 21 Bus. north / SR 41 north (South Alabama Avenue) – Old Courthouse Museum	Northern end of SR 41 concurrency
		43.128	69.408	SR 21 Bus. south / SR 47 south (Pineville Road) / SR 47 Truck ends – Monroeville	Southern end of SR 47 concurrency; northern end of SR 47 Truck concurrency (it ends at this intersection)
	Beatrice	59.336	95.492	SR 265 north (Bryan Street) – Vredenburgh, Camden	Southern terminus of SR 265
	Riley	64.357	103.573	SR 47 north – Greenville	Northern end of SR 47 concurrency
Wilcox	Oak Hill	78.965	127.082	SR 10 – Camden, Greenville
	​	84.111	135.364	SR 28 west – Camden	Eastern terminus of SR 28
	Elm Bluff	85.183	137.089	SR 89 north – Selma	Southern terminus of SR 89
Lowndes	​	102.222	164.510	SR 263 south / CR 7 north – Greenville	Northern terminus of SR 263
	Hayneville	120.503	193.931	SR 97 (Commerce Street) – Lowndesboro, Letohatchee
	​	127.864	205.777	US 80 west (SR 8) – Selma	Southern end of US 80/SR 8 concurrency
Montgomery	Montgomery	138.043	222.159	US 31 south (SR 3) / US 80 east (SR 8) to I-65 – Mobile, Hope Hull	Interchange; southern end of US 31/SR 3 concurrency; northern end of US 80/SR 8 concurrency
		139.276	224.143	US 31 north (West Boulevard / SR 3) / Selma-Mobile Highway – H. Councill Trenholm State Technical College	Northern end of US 31/SR 3 concurrency
		139.836	225.044	I-65 / US 80 west / US 82 west (SR 6 west / SR 8 west) to I-85 – Birmingham, Atlanta, Selma, Mobile, Tuscaloosa	I-65 exit 168; southern end of US 80/US 82/SR 6/SR 8 concurrency
		141.419	227.592	US 331 south (Court Street / SR 9) – Luverne	Northern terminus of US 331; southern end of SR 9 concurrency
		145.315	233.862	US 82 east / US 231 south (Troy Highway / SR 6 east / SR 53 south) – Union Springs, Troy, Ozark, Dothan, H. Councill Trenholm State Technical College	northern end of US 82/SR 6 concurrency; southern end of US 231/SR 53 concurrency
		148.423	238.864	I-85 / US 80 east (SR 8 east) to I-65 – Montgomery, Atlanta, Tuskegee	I-85 exit 6; north end of US 80/SR 8 concurrency
		149.8	241.1	Atlanta Highway - Faulkner University	Interchange; former US 80 east/SR 8 east
		152.883	246.041	To I-65 (via SR 152 west) / Congressman William L. Dickinson Drive – Birmingham, Mobile, Airport, Maxwell AFB Gunter Annex, Alabama National Guard Headquarters	Interchange
Elmore	Wetumpka			To SR 111 / South Main Street	South end of SR 111 Truck concurrency
		163.340	262.870	SR 170 east – Tallassee	Western terminus of SR 170
				Company Street – Downtown Wetumpka Historical District	Former SR 14 west
		163.681	263.419	SR 14 / SR 111 Truck north (Coosa River Parkway / Tallassee Highway) – Prattville, Tallassee, Wetumpka Sports Complex	North end of SR 111 Truck concurrency
		164.428	264.621	SR 9 north (Central Plank Road) – Santuck, Central	Northern end of SR 9 concurrency; southern end of signed portion of SR 9
Coosa	Rockford	188.890	303.989	SR 22
Talladega	Sylacauga	207.585	334.076	US 231 north / US 280 (SR 38 / SR 53) – Airport	Interchange; northern end of US 231/SR 53 concurrency
		209.581	337.288	SR 148 east (3rd Street)	Western terminus of SR 148
	Winterboro	220.745	355.255	SR 76 west	Eastern terminus of SR 76
	Talladega	230.454	370.880	SR 77 north (East Street) – Talladega Superspeedway, International Motorsports Hall of Fame	Southern end of SR 77 concurrency
	Talladega	231.631	372.774	SR 77 south (Haynes Street) – Central Alabama Community College	Northern end of SR 77 concurrency
	Oxford	250.915	403.809	I-20 – Birmingham, Atlanta	I-20 exit 185
		251.266	404.373	US 78 (Hamric Drive / SR 4) – Heflin
Calhoun	Anniston	254.373	409.374	SR 202 west	Eastern terminus of SR 202
		257.596	414.561	US 431 (Anniston Eastern Bypass / SR-1)	Trumpet/cloverleaf interchange
	Jacksonville	267.730	430.870	SR 204 west (Nisbet Street NW) – Angel, Crystal Springs	Eastern terminus of SR 204
	Piedmont	279.471	449.765	US 278 – Gadsden, Cedartown,	Northern terminus of SR 21; Formerly an alignment of SR 200
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

State Route 21 Business
Location	Monroeville
Length	3.2 mi (5.1 km)

The entire route is in Monroe County.

Location	mi	km	Destinations	Notes
Monroeville	0.00	0.00	SR 21 / SR 41 south	Southern terminus; southern end of SR 41 concurrency
	2.2	3.5	SR 47 south	Southern end of SR 47 concurrency
	2.5	4.0	SR 41 north	Northern end of SR 41 concurrency
	3.2	5.1	SR 21 / SR 47 north / SR 47 Truck south	Northern terminus; northern end of SR 47 concurrency; northern terminus of SR 47 Truck
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

State Route 21 Truck
Location	Frisco City
Length	0.5 mi (800 m)

The entire route is in Frisco City, Monroe County.

mi	km	Destinations	Notes
0.00	0.00	SR 21	Southern terminus
0.5	0.80	SR 21	Northern terminus
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

• United States portal
• U.S. roads portal

• Rand McNally: The Road Atlas 2002, Rand McNally and Company 2001 ISBN 0-528-84446-6

• Southeastroads.com web page on SR-21 with photos