All Pokestops and Gyms are pulled from Niantics other AR, Ingress. they are all portals in Ingress.
All portals in Ingress are submitted by the players and approved before going live. They were always supposed to be places that were manmade and artistic or places where knowledge can be found (so libraries, post offices, churches etc). It was also extended to places of charity, plus a few sponsored locations to make money.
Not all portals have been pulled into Pokemon Go, but it's where all the Pokestops and Gyms come from. If you don't have any near you in your area, it's because there weren't any Ingress players in that area.
The ability to add new portals in Ingress was taken away a while ago as the backlog for approvals was too great. It will be interesting to see if they start allowing submissions in Pokemon Go. I can imagine it won't be for a long time though.