I’m not sure what “Flatbush and its environs” is supposed to mean. But I did post a link to the US Census Beureau that states the estimated population of Kings County, NY (aka Brooklyn, NY) for 2005 was greater than 2.5 million people. Again, the implications of this number, or the area it represents is beyond me, and I do not wish to discuss its relevance. I am commenting specifically on the population of Brooklyn NY according to the US Census Bureau.
See the census numbers here http://quickfacts.census.gov/qfd/states/36/36047.html