Generally speaking, sailors (in the sense of professional sailors, not pressed men) would have come from sailing families, that is from port towns or towns that had close access to the sea. That said, within the category of "port towns" there would be some substantial variation -- Bristol, for example, had its local Society of Merchant Venturers agree to provide a fixed number of seamen to the Navy in return for preventing impressment ashore (meaning that Bristol merchant seamen could not be pressed); in Liverpool, which had a weak local government, impressment contributed to the violent reputation of the port. During this period, also, captains were gaining "followings" of men who wished to go with them from ship to ship; those "followings" could be men who were thrown together with the captain by chance, but more often than before were becoming men who were recruited from the captain's home town or county. Most of these were also men from the port towns or areas near ports; London was the nursery of most seamen by virtue of its size, but large numbers of officers and thus men also came from East Anglia and the southern ports. So, no, by no means were all sailors from the west counties or Cornwall (where we get the stereotypical pirate dialect).