Llandyrnog United was formed in 1975 during a meeting of a few villagers in the local pub, The Golden Lion. It is due to this fact that a Golden Lion is displayed on the official club badge. Their first season was played in the Clwyd League Div 4 and they gained promotion at the first attempt. Llandyrnog remained in league Div 2/3 until the end of 1978/79 which saw them promoted as runners up. The club spent over a decade in Div 1 until 1990/91 when they gained promotion to the premier Division. Only one season was spent in this league as Llandyrnog were crowned champions at their first attempt and promoted to the Sealink Alliance. After a lengthy spell in this league Llandyrnog were unfortunately relegated back to the Clwyd League Premier Division where they stayed until 2002/03 until manager John James was appointed and the club gained promotion to the Welsh Alliance. Only one season was spent in this league as the Club gained promotion to the Cymru Alliance for the first time in its history.