- Apr 7 John Joseph of Austria, Spanish general and illegitimate son pf Philip IV of Spain (Regent of Spain 1677-79, Governor of South Netherlands), born in Madrid, Spain (d. 1679)
Christiaan Huygens (1629-1695)
Apr 14 Dutch mathematician, astronomer (discovered Saturn's rings) and scientist (dynamics), born in The Hague, Netherlands
- Apr 23 Jan Commelin, Dutch botanist and director of Hortus Botanicus, Amsterdam, born in Leiden, Netherlands (d. 1692)