I personally would not recommend you leaving the state and heading to MT before filing something with the courts. Although you are free to do so if there is no injunction in place preventing you to leave the state without court or the father's permission, it looks REALLY bad to the judge and looks like you are absconding with the child and trying to alienate the father from the child. Be up front and serve him with the paperwork for relocation in advance and then hold on for the fight of your life, because CO generally frowns on relocation.
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Often a parent will leave with a child and then be served in the new state by the parent who was left behind. Colorado will have jurisdiction over children's issues under six months has passed after you leave this state. Your new state will not acquire jurisdiction until you have resided there for six months. What you really need to do is obtain expert legal counsel to assist you. As Mr. Leroi has pointed out, when there are two functional parents, CO frowns on taking a child away from one parent. Good luck to you.
Something is missing in the facts provided. If Father previously served Mother with a, APR action, which kept her (well, not her, but kept the child) in the state, is that case still going on? Unless it has been dismissed, then there is still an injunction in place preventing either parent from taking the child out of the state. If the case went through to final orders, then the law of Colorado requires that Mother needs either Father's permission or an order from the court before she can make a significant change to the location (including moving a long distance within the state) of the child's residence.
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