Jews (shortned form of "Judeans") are an ethnoreligious group which descend mostly from the Biblical Israelites of Israel, and other people amongst whom they sat in exile and admixtured with (mostly as converts to Judaism, their national religion). They're the nation/ethnicity of Jesus Christ, Kyle Broflovski and his family, and the South Park Jewish Community.
They're frequently mentioned in the series, mostly by Eric Cartman who mocks them in racist manners.
It is important to note, however, that the way Jews are portrayed in the series (Ultra-Orthodox Jews) is not how the mainstream Jews dress, as this way of living (depicted in the series) had started as a cult in Ukraine and Poland in the 15th and 16th Centuries which mimicked the dressings of noble Poles and spreaded due to these type of Jews' migrations elsewhere.
Archaeology-wise, we can tell that the Jews' ancient roots are in the Levantine Iron Age era's Kingdom of Judah and the remnants of the Kingdom of Israel who assimilated into them following the Assyrian destruction of Israel in 722/1 BC; they were later exiled by the Babylonians, who destroyed their 1st Jewish Temple in Jerusalem, to Syria, Iraq, and Iran in 2 phases between 597 BC and 586 BC.
They were allowed to return to Israel and re-establish their ancestral homeland once Cyrus the Great was in throne in 538 BC, this time however being a sub-unit of the Persian Empire rather than a kingdom on and of it's own - and renaming it "Province of Judea".
They maintained their national homeland, through times of severe despair such as the Jewish-Hellenistic war events of Hannukah in 165 BC & 164 BC; and the Jewish-Roman wars which led to the destruction of their 2nd Jewish Temple in 70 AD, till 135 AD when they were stipped off their national rights by the Roman Empire, that also exiled many of them as slaves to Europe and North Africa. They were later subjected to the cruelty of the Byzantine Empire which opted to convert them all to Chrstianity, thus starting to migrate elsewhere to pagan lands, with only a small portion of them remaining in Israel for all the time of the exile.
In 1948, the modern State of Israel was established, and the Jews had returned in their majority to live in the Land of Israel.