Whipple Well offers one of the most complete online databases of California Place Names I've found so far. They currently have 1,860 place names for Monterey County:

Place names beginning with Ab - Es
Place names beginning with Es - Me
Place names beginning with Me - Sa
Place names beginning with Sa - Zu

When looking for a particular place, you may want to review these county boundary comparison maps:

1850 and 2001 County Boundaries
The Changing Counties