April 17, 1907 was a landmark day in American immigration and ancestry. On that single day, immigration officials stationed in the Port of New York processed 11,747 arrivals through the famed Ellis Island receiving station. In the century that has passed, that single day marks the culmination of a peak period for immigrant arrivals through the "Golden Door" to America.
You can find more information about 1907 immigration at: http://ellisisland.org/genealogy/1907.asp
Immigration “Factoids” can be found on: http://ellisisland.org/Eiinfo/Immigration_Factoids.asp
Here is a press release from the Liberty-Ellis Island Foundation concerning events to commemorate the day: