There appears to be various opinions on the subject. Some have suggested neck in this sense came from the Old Breton word cnoch and/or the Old German word hnack, both of which had a sense of "hill" or "summit" to identify a place. Neck has, also, been used in England, since around 1555, to describe a narrow strip of land jutting out into the water, presumably because it resembled an animal's neck. Early American settlers seem to have seen the same animal's neck in a narrow stand of trees or a logged settlement on the edge of a woods. Hence, your "neck of the woods" was your home or neighborhood.