- May 7 Japanese Emperor Kōkaku abdicates in favour of his son Emperor Ninkō
- May 15 Ambonese uprising against Dutch authority (modern Indonesia), under Thomas Matulesia (aka Kapitan Pattimura)
- May 15 First private mental health hospital opens in the US, Asylum for the Relief of Persons Deprived of the Use of Their Reason (now Friends Hospital) in Philadelphia, Pennsylvania
- May 16 Mississippi River steamboat service begins
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