Deseret

Deseret includes the territory formerly known as Utah and all of the darkest-colored counties on this map which are contiguous with Utah, except for the long pokey ones (Navajo, AZ and Rio Blanco, CO) which it has only the nearer half or so of.  While it has freedom of religion within the limits of its other laws (for instance, alcohol is illegal throughout Deseret, so good luck holding a communion with wine involved) it is both overwhelmingly and formally a Mormon state.  There is a secular government but it doesn't hold secularism as a particular virtue, money flows pretty freely between church and state, the church handles things other countries might handle with public welfare programs, etcetera.

Migration

Deseret accumulated Mormons from around the world as things trended more dystopian and religiously controlling.  While there are still Mormons elsewhere in the world in places that are friendly to religious pluralism, Deseret has thriving expat communities from various South American countries, Canada, Australia, Japan, the Philippines, and several European nations.  They are happy to accept tourism but tourists get bothered by missionaries A Lot.

It is legal to emigrate from Deseret; however, if you look like you might be leaving permanently and you didn't get your church authorities on board with your plan, especially if you're moving somewhere without much LDS presence, you are obliged to first spend a couple days talking to missionaries about this decision.  The missionaries will try to find out what isn't working for you about life in Deseret, and try to hook you up with resources to make things work out for you, and try to convince you that God wants you to live in Deseret.

Missionaries

Unlike the real life Mormon church, in Deseret sister missionaries are vanishingly uncommon, since women are often married well before the age at which they'd start, but if someone makes it to age 21 without being married yet she can serve a mission.  Elders (male missionaries) are slightly less common than in real life, as fewer foreign countries welcome them and they still do the "obey the law of the land" thing.  Senior couple missionaries, on the other hand, are more common than in real life - retired married couples jointly performing missionary service.  There are proselytizing missionaries, but missionaries may spend some or all of their time on humanitarian work or administrative church tasks.​  Missionaries also do emigrant exit interviews and some social-work-like functions, including regular meetings with children of non-Mormon families.

Religion

Non-Mormon religions are tolerated in Deseret.  They get bothered by missionaries - a lot - but if you don't mind doing your Shabbat with grape juice and politely turning away a doorbell-ringer twice a week ​you can be Jewish here, they have a small but robust Muslim demographic, etc.  These religions do not enjoy special state protection (the synagogues and mosques have to pay taxes), are not lovingly portrayed in Deseret media, will encounter a lot of ignorance and confusion about their practices, and their adherents are unlikely to ascend to political office (the overwhelming majority votes a straight church endorsement slate, with a few higher-up political offices formally reserved for full-tithe-paying active LDS with temple recommends), but they aren't actively persecuted... unless you count the requirement that they let their kids talk to an LDS missionary pair once a month ages five to sixteen.  The missionaries are mostly there trying to convince the kids to join the LDS church, but they double as religiously-discriminatory child protective services where called for - if you ask your visiting missionary to remove you from your house they will whisk you away and place you with an LDS foster family.

LDS offshoots, most notably the FLDS, are also allowed.  The FLDS are grudgingly permitted to exist, practice, and do the polygamy thing.  The polygamy thing produces a lot of restless teenage boys who have no realistic prospects of getting married since most of the girls have been paired off at age twelve with men in their forties, and these teenage boys are easy pickings for the missionaries.  Sometimes the girls are whisked off too if they don't fancy marrying middle aged men.  If current demographic trends continue the FLDS will cease to exist sometime in 2070 as the older members die off and the remainder fail to have enough children to keep up with attrition.  The FLDS are mad about it.

The LDS will baptize you after you are dead if they can get enough information about who the heck you were to do that.  They have stopped being polite about not doing it to Holocaust victims and suchlike.  Some people spend a lot of time being proxies for these baptisms as a church calling.

If you are a member of the church, instead of missionaries you get home teachers (for families) and visiting teachers (by and for women).  Most people in the church both teach and are taught in this way but more active members will have a higher number of teachees.

Names

Deseret families name kids weird things.  Biblical names are popular especially where held by Mormon historical figures ("Joseph"), but so are names from Mormon scripture ("Nephi"), popular culture especially Mormon-derived ("Luet" - Orson Scott Card exists and wrote similar books but with modified Earth geopolitics), and inventive ​syllable jumbles particularly if they have lots of Ys ("Kaydyn"), plus a few individual names of different provenance that happened to take root in the Deseret imagination ("Brighten").  There are also smatterings of foreign names from the expats that have leaked into the surroundings ("Hélio", "Kairi").

Life Script

​Deseret citizens can get married as early as twelve with parental consent (it's still not very common), and sixteen without.  The Optimally Respectable And Mainstream Life Path for a Deseret girl is to get engaged at sixteen and married at seventeen, to either a boy your age or a returned missionary who will be 20-21.  (Either sort of husband is fine but holding out for a missionary is a social climber sort of thing to do.)  You move in with one or the other set of parents, or university housing if applicable, till your husband has an established income that lets you move out while still tithing (you can also have a job, especially if you know you're infertile or plan to drop it once you have a baby; this is not expected, especially not if your career takes priority over your husband's in your family decision making, but it's not unrespectable, just irregular and noteworthy).  You can go to college but you don't have to and caring too much about it is understood to be kinda classist.  You do Relief Society work and whatever other church callings your bishop hands you.  You have kids if you can and get grandparent and Relief Society help with them.  If you fail at this life path, perhaps because you're picky about husbands or husbands are picky about you, then you can achieve moderate respectability by becoming a sister missionary at age 21 for a year and a half and then trying again to get married.  (This is also a good fallback if you kinda don't want kids and want to give the bitoxiposphene another few years to do its work on you.)

The Optimally Respectable And Mainstream Life Path for a Deseret boy is complement to the above - either get married at 17-18, or wait, start a mission at eighteen, come back and do college if you're gonna do college, and marry a sixteen-year-old (or a script-delayed girl your age).  You do your church callings, you conduct your career honestly and diligently but don't bring your work home with you, you strive to provide for your family, you try to have kids, you raise your kids to follow their life scripts.

In general it is frowned upon to pursue or express individuality by being queer, wearing clothes unlike what everyone else is wearing, having an unconventional family structure or not cultivating your family life at all, or being differently religious or irreligious.  Mainstream Deseretians would say that these are shallow, fake forms of individuality and real individuality comes from engaging deeply with your family and community, and maybe stories that speak to you.  Deseretians might seem weirdly Stepfordian and samey to outsiders but consider those outsiders to be settling for a pathetic facsimile of the real thing.

If you fail at your life script, you will get a mix of your neighbors aggressively Practicing Charity And Forgiveness At You in the hopes that they will be a good example, and people shunning you and cutting you off from opportunities of various kinds because they Just Can't Condone That Sort Of Thing.  If you fail (or suffer bad luck) in a way that means you need help beyond what the occasional casserole from the Relief Society can manage, there is a kind of Basic Jobs Guarantee: you can work at an unskilled church-owned operation, such as a food storage plant or DI (formerly known as Deseret Industries and now named solely by its initialism; mormon goodwill), and earn a limited but livable wage.  If you can't even do that, you can still get pretty good welfare up to and including free housing if your family can't step in there, at the cost of lots of interaction with churchy people.

Children

The age of majority is sixteen for everything.  When you're sixteen you can legally drive, get married without parental approval, live on your own, etcetera.  (There is no drinking age, since alcohol is illegal.)​  The minimum age for marriage with parental approval is 12.

Deseret has "pro-adoption" policy.  Children in questionable circumstances - and "questionable" is a pretty broad brush - can pretty easily be taken away and given to a nice infertile Mormon couple to raise.  (They could be given to a fertile Mormon couple but in practice the social services that place the children pray about it and tend to find that Heavenly Father wants the baby to go to a couple who does not have their own children through no fault of their own.)  The adoptions are typically closed and can be sealed in the temple, spiritually uniting the adoptee with the parents.

Boy Scouting is popular.

Laws

Abortion is illegal in Deseret outside of extreme circumstances where church leaders (at least your stake president - determined geographically even if you are not a church member - and possibly higher-ups) agree; they might agree if the mother will otherwise die, or if the child is the product of rape or incest, and every now and then someone can get one for a fetus that won't survive outside the womb but this is even rarer.

Alcohol, recreational drugs including tobacco, and coffee ​are illegal throughout Deseret.  Tea is grayish-market; technically caffeinated tea is illegal but it's easy enough to smuggle around as "chamomile" that you can pretty much get it if you want it.  You're unlikely to get in serious trouble over coffee you use to flavor your ice cream or chocolate cake, and you can have all the Mountain Dew you want.  They take alcohol and tobacco more seriously.

Divorce is legal with a bishop's recommendation (or higher authority if you are married to the bishop).  Most bishops will rubber-stamp it if you were married in a non-LDS context with dubious consent or a plural marriage, especially if you were under 16 at the time and have been removed from your non-LDS home.  You can also usually get one for spousal adultery, abandonment, or abuse of you or your kids unless your bishop really ships it and wants you to work it out.  It is harder to get a divorce if your marriage has been sealed in the temple, and even if you get one in that case you might not get a cancellation of sealing - women need to have prior sealings cancelled to remarry (even if their husband is in fact dead), but men do not.

Birth control is legal with a bishop's permission.  A doctor's note usually suffices, if you have a medical reason to not want to be pregnant; just not wanting kids will get you reminded that some nice childless couple would want your kid and Heavenly Father might be calling you to provide one.

Non-Mormons still technically "have" Mormon bishops, stake presidents, etc., since these are determined geographically, and are advised to know who they are and how to get ahold of them if they need to

Thanks to the FLDS, polygynous (but not polyandrous) marriage is legal.  It's socially costly to practice or arrange it, but some people do it anyway, especially if they really want children.

There are modesty laws.  Men may not be topless in public.  Women may breastfeed but not otherwise be topless in public.  You may incur minor fines in Deseret for immodesty comparable to a particularly draconian high school dress code (exposed shoulders, short shorts/skirts, crop tops) if you are noticed by a bored police officer.

Homosexual sex acts are a crime for both sexes.  Transition is illegal.  Reparative therapy is the usual response to a queer-seeming minor; a queer-seeming adult will get lots of community concern, but unless they actually get caught doing queer things it's not illegal outright.  (If someone tried to start a GSA or something that would get shut down smart quick though.)  Penalties vary from court-ordered therapy and community service to something like a restraining order against both participants in the sex from getting near each other or even a few months or years in jail for repeat offenders.

The internet is censored at the federal level for pornography and violent media; there's a small industry of editing same out of foreign films.  Most people in Deseret voluntarily install filters that mince swear words (optionally with color coding or other markings so they can know that whoever they're reading is the sort of person who swears).  "Corrupting" sorts of content from countries which do not allow Mormon missionaries is censored ideologically; however, it is considered important to be able to understand the culture of countries which do allow missionaries, so in practice you can access anything you want through a Cascadian or Canadian proxy.