One of the oldest cryptocurrency exchanges is Coinmama. This exchange was created in 2013, and is registered in Slovakia, although the parent company is New Bit Ventures, which has its headquarters in Israel.
Since its inception in 2013 it has spread its wings quite a bit and now offers its services in 217 countries, including Canada, Australia, the U.K. and the U.S., however it is only available in 24 of the 50 U.S. states.
You can also use Coinmama in many European countries as well as across Asia and in Central and South American countries. You can see a complete list of supported countries here to find out if Coinmama works in your country.