From the experts:
Marin is a lovely county north of San Francisco, and a lovely baby name on the rise, one which sounds more refreshing than the more familiar Marina.
As a place-name, Marin is pronounced with the accent on the second syllable, Ma-RIN, sort of like Marie, though when used as a name, many would say MAR-in, to rhyme with Karen.
Marin is unisex in several European countries (in Croatia it's currently Number 29 for boys); Maren is an alternate, Scandinavian, spelling. In France a very fashionable alternative for girls is Marine.