Highway 21 begins at Highway 1 approximately east of
Strathmore in
Wheatland County and travels north, passing near the village of
Rockyford (located about east of Highway 21) and it reaches a
four-way stop at
Highway 9 between
Beiseker and
Drumheller, where it crosses into
Kneehill County. It continues north past the village
Carbon (located about east of Highway 21) to the intersection of
Highway 27 east /
Highway 582 west, beginning
concurrency with Highway 27. Highway 21 continues to the town of
Three Hills, home of
Prairie Bible Institute, passing along the town's eastern edge. North of Three Hills, the CN rail line begins to run parallel to the highway, serving most of the communities along the route. Highway 27 departs from Highway 21 towards
Olds, about south of the town
Trochu. Highway 21 passes the hamlet of
Huxley and the access road to
Dry Island Buffalo Jump Provincial Park before entering
Red Deer County; the Kneehill / Red Deer county boundary also signifies the transition from the
prairie to
aspen parkland ecosystem, with increasing foliage. Highway 21 bypasses
Elnora and
Lousana prior to
Delburne, skirting its western edge on a bypass constructed in the 1980s. North of Delburne, Highway 21 reaches a
T intersection with
Highway 595 and turns east for along Township Road 380, then north at Range Road 231, the former alignment through Delburne. The roadway narrows for the following as it heads towards the
Red Deer River, which it crosses at the Content Bridge. North of the Red Deer River, it briefly enters
Stettler County, crossing
Highway 11 and
Highway 12. Highway 21 intersects
Highway 13 at the locality of
Ervick, about west of the city of
Camrose, home of the
Augustana Faculty of the
University of Alberta (formerly
Augustana University College) and
Big Valley Jamboree; Highway 21 is considered the main north–south highway serving Camrose despite not entering city limits. It continues north past the hamlet of
Armena and village of
Hay Lakes, entering
Leduc County just south of the hamlet of
New Sarepta, into the eastern portion of the
Edmonton Metropolitan Region. North of the hamlet
Looma, it enters
Strathcona County and reaches an
interchange with
Highway 14. It becomes a divided highway, passing along the eastern edge of
Sherwood Park prior to an interchange at
Highway 16. Highway 21 continues north to the city of
Fort Saskatchewan in which it ends at
Highway 15. == History ==