Herennia Etruscilla was an Augusta and later regent of the Roman Empire, married to the emperor Trajan Decius, mother of Herennius Etruscus and Hostilian. As with most third-century Roman empresses, very little is known about her. She was probably from an old senatorial family. Herennia married Decius and gained the title Augusta when Decius became emperor in 249 CE. She acted as regent for her son Hostilian, when Decius and Herennius were defeated and killed in the Battle of Abrittus in 251 CE.