Decimus was a Roman praenomen. It means "tenth", and was originally used as a name for tenth sons, but it was later used as a generic name.
Among those named Decimus were:
- Decimus Clodius Albinus, would-be emperor of the 2nd century AD
- Decimus Junius Juvenalis, a poet of the 1st century AD
- Decimus Junius Brutus Albinus, politician and general of the 1st century BC, assassin of Julius Caesar
- Decimus Junius Silanus Torquatus, consul in AD 53
- Decimus Junius Silanus (Consul 62 BC)
- Decimus Magnus Ausonius, poet and rhetorician of the 4th century AD
Decimus Burton was an English architect of the 19th century.