In the United States, the copyright term, or length of time a work is protected by copyright, for most works is the life of the author plus 70 years. However, there are exceptions for anonymous or pseudonymous works and works made for hire, for which the copyright term is 95 years from the year of first publication or 120 years from a work's creation, whichever comes first. In all cases, copyright protection runs through the end of the calendar year in which the term expires. 

Cornell University Library has a very handy chart that can help you figure out whether a work is still protected by copyright, which is linked below.