Dennis is a masculine given name of Irish and Gaelic origin, derived from the old Irish personal name 'Dónal', which means "dark" or "bold". It is also associated with the Irish god of the underworld, Donn. In medieval Ireland, it was often anglicized to Dennis. The name gained prominence in England during the Middle Ages through the popularity of Saint Denis, an early French martyr whose feast day is celebrated on October 9th. Dennis has been used as a given name for centuries and continues to be popular today. It is also a surname found throughout Europe, particularly in Ireland, Scotland, and England. Some notable individuals with the first name Dennis include American actors Dennis Quaid and Dennis Haysbert, Canadian singer-songwriter Dennis Leeflang, and French football coach Denis Lawrence.
"The name Dennis saw its peak popularity between the years 1939 to 1943, with a significant spike in 1943 reaching 68 births, perhaps influenced by World War II. However, overall, the number of babies named Dennis has been declining steadily since the late 1950s, with only 5 births recorded in 2022."