FROM the reference book:
"From Abbotts to Zurich - New York State Placenames" by Ren Vasiliev:

Moriches, Center Moriches and East Moriches
The name derives from the Native Americans who lived there.
(He cites 3 references for this entry.)

I hope that helps.
Richard
-- 
Richard Frisbie
d/b/a Hope Farm Press & Bookshop
252 Main Street Saugerties NY 12477
History & Genealogy  (NYGenWeb)  http://www.hopefarm.com