Erlandson was born around 1790 in Copenhagen, Denmark. He and his father worked as carpenters in the Copenhagen dockyards, whichdespite Denmark's nominal neutralitywere preëmptively attacked by the United Kingdom during the Second Battle of Copenhagen in 1807, the onset of the Gunboat and Anglo-Russian Wars. In December 1813, amid the War of the Sixth Coalition, Erlandson was captured by the Royal Navy at age 23 while working as a sailor in the Kattegat. He was held in a prison ship in Chatham, Kent. Hostilities between Britain and Denmark ended the next year, and the Hudson's Bay Company hired Erlandson and other Scandinavians to work in northern and western Canada.