- Apr 2 H L Fizeau & Leon Foucault take 1st photo of the Sun
- Apr 10 More than 1,000 buildings damaged by fire in Pittsburgh, Pennsylvania
- Apr 18 Whaling ship the Manhattan captained by Mercator Cooper is the first ship officially permitted visit Edo, Japan, in 220 years rescuing shipwrecked sailors
- Apr 29 Macon B. Allen & Robert Morris Jr are 1st African Americans to open a law practice in the US