Sherlock Holmes is probably more widely recognized than Mormonism. I’m probably not the only person who first heard of Mormonism as the weird backstory in the first Holmes novel,
A Study in Scarlet. Mormonism is represented there as kind of a cross between the Moonies and the Mafia; it provides the twist that makes the murderer sympathetic.
It’s bizarre that so much of the Baker Street detective’s first story is about Mormons in Utah, but evidently lurid tales of violent enclaves in the wild American west sold well for Doyle, because he did another one at greater length in the fourth Holmes novel, in which Holmes is little more than a frame.
It's been a long time since I read ASIS. It introduces Mormonism in a long flashback, by having two characters rescued, years before Sherlock Holmes ever enters the story, by a Mormon wagon train.
Arthur Conan Doyle wrote:“My name is John Ferrier,” the wanderer explained; “me and that little un are all that’s left o’ twenty-one people. The rest is all dead o’ thirst and hunger away down in the south.”
“Is she your child?” asked someone.
“I guess she is now,” the other cried, defiantly; “she’s mine ‘cause I saved her. No man will take her from me. She’s Lucy Ferrier from this day on. Who are you, though?” he continued, glancing with curiosity at his stalwart, sunburned rescuers; “there seems to be a powerful lot of ye.”
“Nigh upon ten thousand,” said one of the young men; “we are the persecuted children of God—the chosen of the Angel Merona.”
“I never heard tell on him,” said the wanderer. “He appears to have chosen a fair crowd of ye.”
“Do not jest at that which is sacred,” said the other sternly. “We are of those who believe in those sacred writings, drawn in Egyptian letters on plates of beaten gold, which were handed unto the holy Joseph Smith at Palmyra. We have come from Nauvoo, in the State of Illinois, where we had founded our temple. We have come to seek a refuge from the violent man and from the godless, even though it be the heart of the desert.”
The name of Nauvoo evidently recalled recollections to John Ferrier. “I see,” he said, “you are the Mormons.”
“We are the Mormons,” answered his companions with one voice.
“And where are you going?”
“We do not know. The hand of God is leading us under the person of our Prophet. You must come before him. He shall say what is to be done with you.”
They had reached the base of the hill by this time, and were surrounded by crowds of the pilgrims—pale-faced meek-looking women, strong laughing children, and anxious earnest-eyed men. Many were the cries of astonishment and of commiseration which arose from them when they perceived the youth of one of the strangers and the destitution of the other. Their escort did not halt, however, but pushed on, followed by a great crowd of Mormons, until they reached a waggon, which was conspicuous for its great size and for the gaudiness and smartness of its appearance. Six horses were yoked to it, whereas the others were furnished with two, or, at most, four a-piece. Beside the driver there sat a man who could not have been more than thirty years of age, but whose massive head and resolute expression marked him as a leader. He was reading a brown-backed volume, but as the crowd approached he laid it aside, and listened attentively to an account of the episode. Then he turned to the two castaways.
“If we take you with us,” he said, in solemn words, “it can only be as believers in our own creed. We shall have no wolves in our fold. Better far that your bones should bleach in this wilderness than that you should prove to be that little speck of decay which in time corrupts the whole fruit. Will you come with us on these terms?”
“Guess I’ll come with you on any terms,” said Ferrier, with such emphasis that the grave Elders could not restrain a smile. The leader alone retained his stern, impressive expression.
“Take him, Brother Stangerson,” he said, “give him food and drink, and the child likewise. Let it be your task also to teach him our holy creed. We have delayed long enough. Forward! On, on to Zion!”
“On, on to Zion!” cried the crowd of Mormons, and the words rippled down the long caravan, passing from mouth to mouth until they died away in a dull murmur in the far distance. With a cracking of whips and a creaking of wheels the great waggons got into motion, and soon the whole caravan was winding along once more. The Elder to whose care the two waifs had been committed, led them to his waggon, where a meal was already awaiting them.
“You shall remain here,” he said. “In a few days you will have recovered from your fatigues. In the meantime, remember that now and for ever you are of our religion. Brigham Young has said it, and he has spoken with the voice of Joseph Smith, which is the voice of God.”
The story soon puts Mormonism in a harsher light, providing a revenge motive that explains how two fugitive Mormon elders ended up murdered in Sherlock Holmes's London. I expect that far more people have first met Mormonism in these quoted paragraphs than by meeting Mormon missionaries. Apart from misspelling Moroni, Doyle's depiction may not be too inaccurate, except in what it omits. I don't recall any mention in ASIS that Mormonism had any connection at all to Christianity.