Neighborhood: Strip District
The original name of 21st Street was Allegheny Street, after the Allegheny River. (See Allegheny River Boulevard for more about the name Allegheny.)
In 1868, Pittsburgh’s modern sequence of numbered streets was created by renaming all the streets perpendicular to the Allegheny River; Allegheny Street became 21st Street.[1, 2, 3]
Cridlebaugh, Bruce S. “Field notes: Changing Pittsburgh street names—from downtown to Lawrenceville.” Pghbridges.com: Bridges & tunnels of Allegheny County & Pittsburgh, PA, Feb. 9, 2000. http://pghbridges.com/articles/fieldnote_pghstnames.htm.
Killikelly, Sarah H. The History of Pittsburgh: Its rise and progress. B. C. & Gordon Montgomery Co., Pittsburgh, 1906, p. 534. DonsList.net HistPgh1909M; Google Books kXmloex-vr8C, poRU0YjqrzsC; HathiTrust 100122020; Historic Pittsburgh 00adc8925m; Internet Archive historyofpittsbu00kill, historypittsbur00killgoog.
“An ordinance changing the names of streets.” Pittsburgh city ordinance, 1868. Passed Aug. 31, 1868. Reprinted in the Pittsburgh Gazette, Sept. 2, 1868, p. 5 (Newspapers.com 86347563), Sept. 3, p. 3 (Newspapers.com 86347623), and Sept. 4, p. 3 (Newspapers.com 86347714).