Samaritans follow Samaritanism, which is sort of a different form of Judaism, and the phrase "Good Samaritan" derives from a parable in the Gospel of Luke (first attested in the 1630s). Samaritans are also traditionally from the region of Samaria. But here's the thing: we're not sure if the Samaritans are named after Samaria, or if Samaria is named after the Samaritans. It's sort of a chicken-and-the-egg kind of question. Even then, the origin is disputed and even politicized (because there's a whole debate over whether the people-group rightfully owns the place). There is a Hebrew cognate which traces back to a word for "to guard", shomer, and the Samaritans' own appellation for themselves is Shamerim, which means "guardians of the Torah", so that probably hints at an etymology which is thereafter uncertain.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.