I have website which is targeting to small geografical area, the bigest CDN companies don't even have CDN servers close to this area. I am wondering will I get any benefit to use CDN, becouse main server will be closer geograficaly?
Quite possibly you might want one anyway.
They tend to be good at not being vulnerable to DDoS, and make it more difficult to find and attack your real servers in many cases.
Not all of the Internet's topology is geographic. If you want to use one, select one which is well-peered to ISPs which serve your target market.