The given name Denzil has its origins in the Celtic language. It is believed to have derived from the Old Welsh name Dingad, which means "valiant" or "brave." The name was most prevalent in Cornwall, a region in southwestern England with strong Celtic roots.

Denzil gained popularity during the Middle Ages, particularly among the gentry and nobility of Cornwall. One of the earliest recorded instances of the name can be traced back to the 12th century, when Denzil de Wolveton, a knight from Cornwall, was mentioned in historical records.

In the 13th century, the name Denzil appeared in the Domesday Book, a comprehensive record of landholdings and properties in England commissioned by William the Conqueror. This suggests that the name had become well-established in the region by that time.

Throughout the medieval period, the name Denzil was associated with chivalry and bravery, reflecting its Celtic origins. Several notable individuals bore this name, including Denzil Holles (1599-1680), an English nobleman and political figure who played a significant role in the English Civil War.

Another famous bearer of the name was Sir Denzil Onslow (1690-1776), a British politician and Speaker of the House of Commons. He was widely respected for his impartiality and fairness in presiding over parliamentary debates.

In the literary realm, Denzil Holles Carnaby (1804-1877) was an English author and poet who wrote several works, including "The Poetical Works of Denzil Holles Carnaby."

During the 19th century, the name Denzil was particularly popular among the upper classes in England, with several prominent figures bearing the name. One notable example was Denzil Charles Jelf Ibbetson (1819-1891), a British army officer and explorer who served in India and Afghanistan.

Another famous individual with the name was Denzil Onslow Yorke (1866-1944), a British army officer and author who served in the Boer War and World War I. He wrote several books, including "The History of the British Navy" and "The Household Cavalry in Peace and War."

While the name Denzil has its roots in the Celtic language and was most prevalent in Cornwall, it has since spread to other parts of the English-speaking world, though it remains relatively uncommon.