 State Route 21 | ||||
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| Route information | ||||
| Maintained by ALDOT | ||||
| Length | 279.471 mi[1] (449.765 km) | |||
| Major junctions | ||||
| South end |  SR 97 at the Florida state line | |||
 US 31 in Atmore and in Montgomery I-65 north of Atmore and again in Montgomery US 84 in Monroeville US 80 in rural Lowndes County and again in Montgomery US 82 in Montgomery I-85 in Montgomery US 280 in Sylacauga I-20 in Oxford US 78 in Oxford US 431 in Anniston | ||||
| North end |  US 278 at Piedmont | |||
| Location | ||||
| Country | United States | |||
| State | Alabama | |||
| Counties | Escambia, Monroe, Wilcox, Lowndes, Montgomery, Elmore, Coosa, Talladega, Calhoun | |||
| Highway system | ||||
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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.