The closest language to Latin was Faliscan, spoken nearby probably until about 150 AD. Faliscan differed from Latin in a few respects: e.g.
“f” instead of “b” between vowels (some Romance languages later changed “b” to “v” themselves: Portuguese cavalo from Latin caballu-)
the reduction of “di” to “i” (this also happened in some Romance languages later — e.g. Spanish hoy from Latin hodie)
the loss of final “s” (this was seen in graffiti at Pompeii, and is also a feature of Italian and Romanian: Italian (tu) ami, (voi) amate from Latin amas, amatis)
a contrast of Latin “qu” with Faliscan “p” (this is a common issue in Indo-European languages, e.g. Welsh pump versus Latin quinque versus proto-Germanic *fimfi “five”).
Thus, Latin may be regarded as the direct descendant of a common proto-Latino-Faliscan language, in the same way that English derives from a North Sea (Ingvaeonic) dialect of West Germanic. A couple of other dialects were also part of this language group: Lanuvian, Praenestine. Some also argue for Venetic and Sicel.
Latino-Faliscan is conventionally regarded as a member of the Italic branch of the Indo-European family of languages. Whether there was one Italic branch, or two separate branches of I-E (Latino-Faliscan and Osco-Umbrian or Sabellian) has been a point of dispute, which makes it uncertain whether Latin descended from a hypothetical proto-Italic language (see Latino-Faliscan languages – Wikipedia).
Latin, like most languages in Europe (except Basque and the Finno-Ugric languages of Hungary, Estonia, Finland, and Karelia), ultimately descended from the proto-Indo-European language, spoken it is generally believed north of the Black Sea around 4000–5000 BCE.