- May 1 José Amador de los Ríos, Spanish historian and poet, born in Baena, Spain (d. 1878)
Karl Marx
May 5 Karl Marx, German philosopher (Communist Manifesto, Das Kapital), born in Trier, Prussia (d. 1883)
Karl Marx
- May 20 William George Fargo, founder (Wells Fargo)
- May 25 Jacob Burckhardt, Swiss cultural historian, born in Basel, Switzerland (d. 1897)
- May 27 Amelia Jenks Bloomer, American reformer who campaigned for temperance and women’s rights, born in Homer, New York (d. 1894)
- May 28 P. G. T. Beauregard, American Confederate general (Hero of Sumter), born in St. Bernard Parish, Louisiana (d. 1893)
- May 31 John Albion Andrew, American politician (25th Governor of Massachusetts), born in Windham, Massachusetts (d. 1867)