Each year, LIPA, as successor to LILCO, publishes a report (the report is published by LIPA, but is written by KeySpan, previously known as LILCO) updating the census population numbers (by using people-per-electric meter ratios) for all the 292 communities on Long Island.
There are 2 cities and 13 towns (as well as 2 Indian reservations) in the bi-counties and the 13 towns (3 in Nassau and 10 in Suffolk) are further sub-divided into 95 villages and 195 hamlets, yielding 292 communities (2 + 95 + 195 = 292).
The heart of this 40-page report are maps of each of the 13 towns (3 in Nassau, 10 in Suffolk), showing the true borders of all villages and hamlets (not the postal zone borders) in each town. The facing pages list which communities are villages or hamlets and their populations. (You'll find villages and hamlets that you never knew existed because they are in some other community-named postal zone.)
I consider this the best resource available in understanding the geography and governmental organization of Nassau and Suffolk Counties.
The following are the instructions to obtain a copy of the 1998 or 1999 LI Population Survey (I prefer the 1998 version as it was converted into Adobe Acrobat better than the 1999 version was converted):
First, the report is in Adobe Acrobat format (*.pdf) and thus you will need
Adobe Acrobat to open the file. You can obtain a free copy of Acrobat Reader
(1.7 mb storage space required) by clicking on:
Once you have Acrobat Reader, then go to:
Once at the Suffolk Web site, click on the button for GOVERNMENT and then at the GOVERNMENT page, click on the button for the LI Population Survey.
The Population Report is 1,672K and takes about 5 minutes or so to download.