In the 1870s, Little Germany, or Kleindeutschland, ranged from Division Street on its southern end (Division is just below Canal Street) to 14th Street on the north, and from the Bowery on the west to Avenue D on the east. That’s a lot of German surface area! Tomkins Square Park was the center.
The Lower East Side Preservation Initiative has a nice history of the area on its website.
Already contracting by the late nineteenth century, the community suffered a devastating blow on June 15, 1904, when more than 1,000 of its residents were killed in the sinking of the General Slocum in the East River. That was, and remains, one of the biggest tragedies in New York City history.
If you look hard enough in the East Village, you can still find some remnants of Little Germany’s past, described in this 2010 blog entry.