John von Neumann died at the age of 53 at Walter Reed Army Medical Hospital in Washington, D.C., from cancer. He was buried at Princeton Cemetery. This date marks the end of the life of a monumental figure in mathematics, science, and technology.

John von Neumann was present as an eyewitness to the first test of an atomic bomb detonation, code-named Trinity. The event was conducted as a test of the implosion method device, at the Alamogordo Bombing Range in New Mexico. Based on his observation alone, von Neumann estimated the test had resulted in a blast equivalent to 5 kilotons of TNT (21 TJ) but Enrico Fermi produced a more accurate estimate of 10 kilotons by dropping scraps of torn-up paper as the shock wave passed his location and watching how far they scattered. The actual power of the explosion had been between 20 and 22 kilotons. It was in von Neumann's 1944 papers that the expression 'kilotons' appeared for the first time.

John von Neumann married Klára Dán, who remained his wife until his death. This date marks the beginning of Von Neumann's second marriage.

John von Neumann divorced his first wife, Marietta Kövesi, who had studied economics at Budapest University. They had one daughter, Marina, who would later become a professor. This date signifies the end of Von Neumann's first marriage.

Emperor Franz Joseph elevated John's father, Neumann Miksa, to the Hungarian nobility for his service to the Austro-Hungarian Empire. The Neumann family acquired the hereditary appellation Margittai, meaning 'of Margitta' (today Marghita, Romania). Neumann János became margittai Neumann János (John Neumann de Margitta), which he later changed to the German Johann von Neumann. This event represents a shift in the family's social standing and John's formal name.

John von Neumann was born in Budapest, Kingdom of Hungary (then part of the Austro-Hungarian Empire). He was born to a wealthy, non-observant Jewish family and was named Neumann János Lajos. This date marks the beginning of the life of a brilliant mathematician, physicist, computer scientist, and polymath who would make significant contributions to various fields.