All three were born in Ulster (then part of the Kingdom of Ireland) and emigrated to the American colonies in the 18th century. Their Irish birthplaces are documented in official U.S. government and academic records. These three names are historically secure and widely accepted.

Beyond the three Irish-born signers, historians estimate that several others among the fifty-six had Irish or Ulster-Scots ancestry. The precise number varies - often cited as between eight and ten - because definitions differ and 18th-century records are incomplete.

Among those commonly described in reputable historical writing as
having Irish or Ulster connections are:

• Thomas McKean (Ulster-Scots roots)
• Edward Rutledge (family of Irish background)
• Charles Carroll of Carrollton (of Anglo-Irish descent; born in Maryland to an Irish
  Catholic family whose grandfather emigrated from Ireland)
• George Read (often cited as of Irish descent)
• Thomas Lynch Jr. (occasionally described as having Irish roots; documentation
  less definitive)