The name reached its all-time peak in 2004 with 25 births ranking #5102. FALLING Recent data shows the name is currently falling.
Dennis is the familiar English form of a Greek-rooted name meaning "devoted to Dionysus". In modern use, the classical mythological root matters much less than the name's long, stable history.
The name spread through Christian tradition, especially through Saint Denis and later forms across Europe. In English it became a dependable twentieth-century classic.