Letter #165 (1955)
„My name is TOLKIEN [not -kein]. It is a German name [from Saxony], an anglicization of Tollkiehn, i.e. Tollkühn”Letter #324 (1971):
„Possibly the reason why my surname is now usually misspelt TOLKEIN in spite of all my efforts to correct this – even by my college-, bank-, and lawyer's clerks! My name is Tolkien, anglicized from Tol(l)kiehn = tollkühn, and came from Saxony in the 18th century. It is not Jewish in origin, though I should consider it an honour if it were”Unpublished letter to H. Cotton Michin (1956 – source):
„But names are often not derived from what seem obvious sources. My own name comes ultimately and long ago from German tollkühn, and perhaps a trace of the remote ancestral 'rashness' has been inherited. But I am a Westmidlander”
NOTE: Tolkien might have not known the works of the "Baltists" like Trautmann or Gerullis who wrote about the personal- and place-names with the Baltic element tolk- (it might have been the reason why he was so surprised when Mrs. Edit R. Ehrhrardt wrote to him about this etymology in 1973). Maybe in a German source the Tolkien family name was labelled "Low Saxon" (this is the equivalent of the linguistic term "Low German") and Tolkien found it and for the rest of his life claimed that his family came to England from Saxony? In fact Gdańsk and East Prussia are the areas of the Low Saxon (= Low German) dialects.