Decimus may refer to:

• 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 (c. 81 BC–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) (fl. 70–62 BC)
• Decimus Junius Silanus (translator of Mago) (fl. 2nd century BC)
• Decimus Laberius (c. 105 BC–43 BC), Roman eques and writer
• Decimus Laelius (fl. 1st century BC), Roman lawyer and tribune of the plebs
• Decimus Laelius Balbus, consul in 6 BC
• Decimus Valerius Asiaticus (c. 5 BC–47 AD), Roman senator
• Decimus Valerius Asiaticus (Legatus) (35-after 69 AD), Roman senator, Legatus of Gallia Belgica
• Ausonius (Decimus Magnus Ausonius, c. 310–c. 395), Roman poet and rhetorician
• Balbinus (Decimus Caelius Calvinus Balbinus, c. 165–238), Roman emperor in 238
• Clodius Albinus (c. 150–197), Roman usurper
• Juvenal (Decimus Junius Juvenalis), poet of the 1st century AD

• Decimus Burton (1800–1881), English architect
• Decimus Govett (1827–1912), Anglican priest

• Thomas Chatterton (1752–1780), English poet