John Loudon is the name of:
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John Loudon (politician) (1866–1955), Dutch foreign minister (1913–1918)
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John Claudius Loudon (1783–1843), Scottish botanist
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John William Loudon (born 1967), Missouri state senator
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John Loudon McAdam (1756–1836), Scottish inventor of the Macadam Road Surface
{{hndis, name=Loudon, John