Decimus may refer to:
Romen praenomen Decimus (praenomen) Decimus Carfulenus (died 43 BC), Roman statesman Decimus Haterius Agrippa (died 32 AD), consul in 22 AD Decimus Junius Brutus (consul 77 BC) Decimus Junius Brutus Albinus (–43 BC), Roman politician and general, assassin of Julius Caesar Decimus Junius Brutus Callaicus (180 BC–113 BC), Roman politician and general Decimus Junius Silanus Torquatus (16 AD–64 AD), consul in AD 53 Decimus Junius Silanus (consul) () Decimus Junius Silanus (translator of Mago) () Decimus Laberius (–43 BC), Roman eques and writer Decimus Laelius (), Roman lawyer and tribune of the plebs Decimus Laelius Balbus, consul in 6 BC Decimus Valerius Asiaticus (–47 AD), Roman senator Decimus Valerius Asiaticus (Legatus) (35-after 69 AD), Roman senator, Legatus of Gallia Belgica Ausonius (Decimus Magnus Ausonius, –), Roman poet and rhetorician Balbinus (Decimus Caelius Calvinus Balbinus, –238), Roman emperor in 238 Clodius Albinus (–197), Roman usurper Juvenal (Decimus Junius Juvenalis), poet of the 1st century AD
Given name Decimus Burton (1800–1881), English architect Decimus Govett (1827–1912), Anglican priest
Pen-name Thomas Chatterton (1752–1780), English poet