The name Keilor is believed to have originated from the Celtic language, specifically from the Brittonic branch of the Celtic languages. It is thought to be derived from the Welsh word "caer," which means "fort" or "stronghold," and the suffix "-lor," which may be related to the word "llwr," meaning "ground" or "floor." Together, these elements suggest that the name Keilor may have initially referred to a fortified settlement or a place of defense.

One of the earliest recorded uses of the name Keilor can be traced back to the 6th century in ancient Wales. It is mentioned in the Welsh Triads, a collection of traditional stories and historical references, as the name of a legendary figure associated with the kingdom of Powys. However, the exact details surrounding this individual are obscure and shrouded in the mists of time.

Throughout the Middle Ages, the name Keilor appeared sporadically in various Welsh and English historical records, though it was not widely prevalent. One notable bearer of the name was Keilor ap Rhys (born around 1240), a Welsh nobleman and military leader who fought alongside Prince Llywelyn the Last in the struggle against English rule during the late 13th century.

In the 16th century, a man named Keilor Griffith (born circa 1520) gained recognition as a skilled architect and stonemason in the town of Abergavenny, Wales. He is credited with the construction of several notable buildings, including the Market Hall and the Priory Church, which still stand today as testament to his craftsmanship.

Moving forward to the 17th century, Keilor Williams (1620-1689) was a Welsh scholar and clergyman who served as the rector of Llanfair Dyffryn Clwyd in Denbighshire. He is remembered for his contributions to the study of Welsh language and literature, as well as his efforts in preserving historical documents and manuscripts.

Another notable figure bearing the name Keilor was Keilor Jones (1765-1838), a Welsh industrialist and entrepreneur. He played a significant role in the development of the coal mining industry in South Wales, establishing several successful collieries and contributing to the economic growth of the region during the Industrial Revolution.

While the name Keilor has remained relatively uncommon throughout history, it has persisted as a unique and intriguing name with deep roots in Welsh culture and heritage. Its origins can be traced back to ancient Celtic traditions, and it has been borne by individuals who have left their mark in various fields, from warfare and architecture to scholarship and industry.