@bg1234 --
When you move to Montana and establish it as your main, primary home (your domicile in tax terminology), all your income becomes taxable by Montana, regardless of where you earn it.
https://mtrevenue.gov/2021/03/23/montana-residency-guide/#:~:text=You%20are%20a%20Montana%20resident....
Your Montana tax obligations are not based on whether or not your employer "has payroll established" there.
If your employer does not withhold Montana state tax from your pay after you become a Montana resident, you'll have to make quarterly estimated tax payments to Montana.
https://montana.servicenowservices.com/citizen/kb?id=kb_article_view&sysparm_article=KB0013201
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
