Event of Interest
May 5 Indian Wars: Sitting Bull leads his band of Lakota into Canada to avoid harassment by the United States Army under Colonel Nelson Miles

Sitting Bull
- May 7 Cincinnati Enquirer first uses term "Bullpen" to indicate foul territory
- May 8 1st Westminster Dog Show held
- May 9 Mihail Kogălniceanu reads, in the Chamber of Deputies, the Declaration of Independence of Romania. This day becomes the Independence Day of Romania.
- May 12 Ottawa Rough Riders 1st outside competition vs Britannia
- May 13 Caesar Franck's "Lesson Eolides" premieres
- May 16 May 16, 1877 political crisis in France.
- May 17 Edwin T Holmes installs 1st telephone switchboard burglar alarm
- May 22 3rd Kentucky Derby: Billy Walker aboard Baden-Baden wins in 2:38
- May 24 5th Preakness: C Holloway aboard Cloverbrook wins in 2:45.5