George Dettmer (1740-1833) was a London piano maker with a workshop located at 50 Upper Marylebone Street, Fitzroy Square. There is little information about this maker, but his son, William Dettmer (1775-1858) is known to have been a partner in the firm. The workshop remained at 50 Upper Marylebone Street until 1846, whereafter the workshop was located at 60 Warren Street. In 1840s, following financial problems, William Dettmer emigrated to Australia to continue the business until his death.
Palmieri, R. and Palmieri, M., 2003. Encyclopedia of Keyboard Instruments. 2nd ed. New York: Routledge, p.108.