Allow me to put in a plug for the Research Library at the Old York Historical Society Museums.
Researching family history in Maine has been, for me, more difficult in working in neighboring New Hampshire and Massachusetts. There seems to be less centralized information.
I spent the day at the Research Library for The Museums of Old York recently and found there materials and persons helpful in digging through information. They seem to have a pretty good collection of published information. I copied quite a bit from the books 'The Vital Records for the Town of York' and 'The Vital Records for the Town of South Berwick'. They also had some source material ~ at one point, we reviewed what appeared to be the original tax records from the 1840's - 1850's.