Green’s Dictionary of Slang

(US) that area of a town predominantly populated by German immigrants or their descendants.

1878		N.Y. Times 4 Feb. 4/6: Certain localities in large cities are already so far foreign reservations that they are known as ‘Dutch-town,’ ‘Limerick’ or ‘Little Africa’ as the case may be.
1881		N.-Y. Trib. 7 Jan. 8/4: In that part of Brooklyn known as ‘Dutchtown’.
1969		in DARE.