The biggest Jewish communities in the New York City region are:
Rockland County - Monsey, Spring Valley, New City
Westchester County - Scarsdale (Weaver Street & Stratton Rd); New Rochelle (Quaker Ridge Rd. north to Scarsdale border); also there is an othodox shul on North Ave. near Pelham Rd.; White Plains (Old Mamaroneck Rd)
Nassau County - Great Neck, Hewlett, Woodmere, Jericho, Syosset
I know there are synagogues in Bayside (Queens County). Also northern New Jersey has a sizable Jewish population.
You should go to www.walktoshul.org to locate neighborhoods.