U.S. 21 is an original 1927 route. It shows up on preliminary ('25-26) U.S. highway schemes as well, with slightly different routings. 21's original routing coincided with that of the original N.C. 26 until 1933, when 26 was reassigned as part of the state's great renumbering.  In Mecklenburg County, 21 originally entered the state on Rock Hill-Pineville Road (today's N.C. 51), then upon entering Pineville turned north onto Polk Street.  Between Pineville and Charlotte, 21 originally ran over what's now called Old Pineville Road. By 1952 a "New Pineville Road" was built south of Scaleybark Road, and 21 was routed over it instead. Eventually (1950s?) "New Pineville Road" was renamed as an extension of South Boulevard.  Through downtown Charlotte, 21 has had at least two different alignments:    Until about 1935, 21 ran over South Boulevard, Morehead Street, Tryon Street, 11th Street, Graham Street and Statesville Avenue. (11th doesn't run all the way between Tryon and Graham anymore; ramps for I-277 get in the way.)   From about 1936 to the mid-1970s, 21 ran over South Boulevard, Morehead Street, Graham Street and Statesville Avenue. The 1952General Drafting map at right shows this routing.

Substantial parts of 21 were rerouted over Interstate 77 once that Interstate was opened. First, around 1965, a mostly-freeway bypass was built east of Jonesville and Elkin. The entire bypass became part of U.S. 21, leading to the creation of Business 21 through Elkin. The southernmost four miles of this bypass would eventually become I-77 from exit 79 to 83. 

In 1969, 77 was opened between exits 28 and 33, along 21's prior alignment. Also around 1969, the southernmost few miles of I-77 in the state were completed, from the state line probably to Woodlawn Road in Charlotte. At this time 21 was signed over the Interstate, and U.S. 521 was extended northward over 21's old South Boulevard alignment. Note that north of Woodlawn(?), U.S. 21 would continue to be signed over Charlotte surface streets for several years. 

Around 1975, when 77 was entirely completed through Charlotte, 21 was routed over the Interstate all the way north to Sunset Road (exit 16). Today, 21 jogs along a short stretch of Sunset between the Interstate and Statesville Road. The streets over which 21 had been routed went unnumbered. 

The hillclimb up the Blue Ridge has been straightened out over the years, and parts of the original alignment are still visible. This short stretch is a tad twisty, and because of the intermittent hillclimb lane, wide-open, but there's nothing too exciting here. 

Evidence exists of 21's original Charlotte routing: one eating establishment on South Boulevard is still called the South 21 Drive-In. 

For real, re-sign 21 all the way north to Cleveland; to hell with Ohio 21 and 821 and W.V. County 21.

U.S. 121 was signed entirely over the original N.C. 66. Some earlier maps, however, have 121's southern terminus in W-S, not Lexington. 

By 1935, 121 was superseded by U.S. 52, a much longer road in the state and in the nation.