If you mean that beautiful cobalt blue, a very deep blue, your glass has a huge following. You can identify what you have with a little investigation. Are there any marks on the bottom? Is the glass dishware, drinking glasses, or bottles?
If you have bottles, there is a ton of information out there. If you mean glassware for home use, and if it is old there are books out there for you to peruse. "Cobalt Blue Glass Edition" by Monica Clements. If you think that it's Depression Glass try " Depression Glass: A Collector's Guide" by Doris Yeske; or " Warman's Depression Glass Handbook - Identification, Values, Pattern Guide" by Ellen Schroy.