Other
- John Clark (chaplain) (1784–1853), American clergyman who served as chaplain of the senate
- John Allen Clark (1926–2001), British businessman
- John Howard Clark (died 1878), editor of The South Australian Register, 1870–1877
- John James Clark or J. J. Clark (1838–1915), Australian architect
- John Kinzie Clark (1792–1865), trader, trapper and early settler in the Chicago area
- John Kirkland Clark (1877–1963), New York City assistant district attorney
- John Porter Clark (1905–1991), American architect
- John W. Clark (architect), American architect
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