Caernarfonshire Day is November 28th, the date of the death of Owainn Gwynedd

,  chosen because the date of his birth is not recorded.

Owain Gwynedd was the first to be styled “Prince of Wales” and is considered the most successful of all the North Welsh princes prior to his grandson, Llywelyn the Great

Following the adoption of Owain’s attributed arms as the county flag, the recognition of a significant date associated with him as the county day, followed as a natural choice.