Since you are working remotely in WA and you have a single member LLC even though the LLC was formed in MT, you will not have a MT state income tax return related to your MT formed LLC unless you derive some of your LLC's income from MT. This is due to the fact that the MT department of Revenue follows the same guidelines as the federal government when it comes to treating a single member LLC as a disregarded entity for income tax filing purposes.
Please note that Montana requires LLCs to file an annual report between January 1 and April 15 but no MT state income tax return need to be filed in MT in all income for the LLC comes from sources outside MT.
