Here is some general information about copyright. Note: Whether the work is under copyright or in the public domain, always cite your sources! Want to ask for permission to use a work you find on the Internet? Always ask: "Do you hold the copyright for this work?"
General Copyright Overview: See U. S. Copyright Office for more information
More about music and copyright can be found at the Music Librarians Association FAQ
This information is not meant to offer legal advice
Small, John. (1985, September). J. C. Bach goes to law. The Musical Times, 126(1711), 526-529. https://www.jstor.org/stable/964456
“John Christian Bach, born 250 years ago this month, is best known as one of the leading composers of his day. But he has another claim to fame ...: he brought the first legal action for breach of musical copyright… "