The area code 976 has not been assigned to a city or state as of September 2014. It is an area code that is designated to the United States.
There is a list of area codes that have been created but have not been assigned to specific areas. These are created for future purposes when an area gets so populated that a new area code is needed. A person can look up the city and state an area code is assigned to online through a number of web pages. As of 2014, AreaCode.org is one of these pages that is both accurate and up to date.