John Loudon

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