Generally speaking, trusts are valid across the country. That means the trust beneficiaries can be located in any state or move to any state, as can the trustee.
In fact, a recent nj.com article addresses this very matter, in “Is a trust valid in all states?” According to the article, were there an issue that led to litigation, the litigation would be in the state identified in the trust.
Your estate planning attorney will have included a clause along the lines of "Governing law: This agreement and the trusts established hereunder shall be governed by the laws of the State of Missouri."
Likewise, the trust will be taxed pursuant to the laws of the governing state.
Most trusts won’t wind up in a legal fight over their terms or the trustee’s actions, and the trustees are rarely required to appear in court in the home state.
There are some exceptions, such as in the event of a death of the trustee, the trustee resigns, or for whatever reason stops acting as the trustee, and there’s no successor trustee named in the trust agreement. In those situations, a legal action needs to be brought in the home state for the appointment of a successor trustee.
If for any reason there was a need to amend the terms of the trust agreement after the trust maker’s incapacity or death, then such a proceeding would need to be initiated in the state governing the trust agreement.
Some attorneys will add a clause to trust agreements that stipulates that the trustee has the authority to apply to transfer the trust to another estate, if the trustee relocates and if in his or her opinion, the laws of the new state are more favorable for the purposes of the trust.
Reference: nj.com (May 19, 2017) “Is a trust valid in all states?”