Josef Kajetán Tyl was the first-born son of Jiří Tyl, a tailor and retired military band oboe player, and his wife Barbora née Králíková, daughter of a miller and groats maker. He was christened "Josef František", yet this name was changed into Josef Kajetán when he underwent confirmation at the age of eleven. The family surname had several written forms – Tylly, Tylli, Tilly or Tyll – and was later changed to Tyl. Josef Kajetán had four younger siblings: one brother and three sisters, but except sister Anna none of them survived to adulthood.