Actually St. Jerome used the older Latin Vulgate (Vetus Latina) as the basis for many of the books. The origins of Vetus Latina are mostly unknown.
Good point. Thank you for the correction!
Here is a listing of the source documents:
Jerome’s independent translation from the Hebrew: the books of the Hebrew Bible, usually not including his translation of the Psalms. This was completed in 405.
Translation from the Greek of Theodotion by Jerome: The three additions to the Book of Daniel; Song of the Three Children, Story of Susanna, and The Idol Bel and the Dragon. The Song of the Three Children was retained within the narrative of Daniel, the other two additions Jerome moved to the end of the book.
Translation from the Septuagint by Jerome: the Rest of Esther. Jerome gathered all these additions together at the end of the book of Esther.
Translation from the Hexaplar Septuagint by Jerome: his Gallican version of the Book of Psalms. Jerome’s Hexaplaric revisions of other books of Old Testament continued to circulate in Italy for several centuries, but only Job and fragments of other books survive.
Free translation by Jerome from a secondary Aramaic version: Tobias and Judith.
Revision by Jerome of the Old Latin, corrected with reference to the oldest Greek manuscripts available: the Gospels.
Old Latin, more or less revised by a person or persons unknown: Baruch, Letter of Jeremiah, 3 Esdras, Acts, Epistles, and the Apocalypse.
Old Latin, wholly unrevised: Epistle to the Laodiceans, Prayer of Manasses, 4 Esdras, Wisdom, Ecclesiasticus, and 1 and 2 Maccabees.