Montana is a purely "no-fault" divorce state, meaning that you can't allege that your spouse's wrongdoing was the cause of the divorce. Instead, most divorces are based on the grounds that the parties have irreconcilable differences that have led to the breakdown of the marriage, or you can base your divorce on the fact that you've been separated from your spouse for at least six months. However, fault may be considered by the court as a factor in dividing property or awarding alimony. To learn more about Montana's use of fault as a determining factor in alimony and property issues, see Nolo's Essential Guide to Divorce, by Emily Doskow (Nolo).
At least one spouse must be a resident of Montana for 90 days before filing for divorce.
Montana is an equitable division state. In an equitable division state, each spouse owns the income he or she earns during the marriage, and also has the right to manage any property that's in his or her name alone. But at divorce, whose name is on what property isn't the only deciding factor. Instead, the judge will divide marital property in a way that the judge considers fair, but won't necessarily be exactly equal.
Like all states, Montana courts begin with a presumption that it's best for a child to have frequent and continuing contact with both parents after a divorce. If possible, judges want to support joint custody arrangements. However, the exact nature of the time-share will be determined by the children's best interests. For more information, see Nolo's article Child Custody FAQ.
Like all states, Montana requires both parents to support their children, even after a divorce. The amount of child support depends primarily on each parent's income and other resources, and how much time each parent spends with the children. In addition, sometimes the courts will "impute" income to a parent who has the capacity to earn more than he or she actually is earning. To learn more about child support, see Nolo's Child Support area.
Yes. You can usually get fill-in-the-blank forms at your local courthouse or the local law library. And you can go to this online resource for Montana, where you'll find extensive information about do-it-yourself divorce, along with court forms (in some states).