May 31, 1790 was the date the first U.S. copyright law was enacted. The law was much more limited than today’s copyright law. Copyright lasted for 14 years, with the possibility of a 14 year renewal. It applied only to books, maps, and charts. Today’s copyright lasts for life of the author plus 70 years (95 years from publication for a work of corporate authorship), and applies to pretty much anything that is fixed (saved, written down, painted, etc) and that shows a modicum of creativity.
The U.S. Copyright Office has an interesting timeline that shows the history of copyright law from 17oos to today. You can also check out our Copyright Crash Course for more information about copyright. If you are interested in making your own copyrighted works more reusable, then check out our Creative Commons LibGuide.