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William Parsons (surveyor) (1701–1757), Surveyor General, founder of Easton, Pennsylvania •
William Barclay Parsons (1859–1932), American civil engineer •
William E. Parsons (1872–1939), American architect and city planner •
William Sterling Parsons (1901–1953), American naval officer and atomic bomb weaponeer aboard
Enola Gay •
William W. Parsons (academic administrator) (1850–1925), president of Indiana State Normal School, later known as Ball State University •
William W. Parsons (NASA), former director of the NASA John F. Kennedy Space Center, & Space Shuttle Program manager •
William Henry Parsons (New York activist) (died 1935), headed the New York Society for the Suppression of Vice •
William Henry Parsons (colonel) (1826–1907), American newspaper editor, legislator, and Confederate colonel