Spelling variations the family name include: DeMeer, DeMar, Deemer, Deamer, Demer, Diemer and many more.
Some of the variations are the result of Anglicizing names when settlers arrived in English colonies. The immigrants would tell their name to an official who would record the name using an English spelling. This also occurred on early census records and on ship lists. Hence the German Diemer would have become the English form, Deemer. Most early records are handwritten. Unfortunately it is often difficult to distinguish between Deemer, Diemer, Deamer, Deaner, Diener, and other variations. Many early records that appear to be recorded as Diener, or other variants, are in reality Deemer.
The American Deemer name appears to be derived from the German name, Diemer, although the name also appears in England. The British variation of DeMar goes as far back as the 10th century and earlier. One of the seven ancient kingdoms of Scotland was ruled by the Earl of Mar. Donald, Earl of Mar (aka, Donald de Mar) fought with the King of Scotland against Viking invaders in 1014. Kildrummy Castle was the seat of Clan Mar and is believed to have been built during the lordship of Donald. It is likely that the British Deemer surname originates with the Clan Mar. There is no evidence of British Deemers emigrating to America.