Trust Situs

Prior accountant filed the first year trust return as a Florida trust. Client comes to us now and we're not sure if we can maintain the Florida Situs. The grantor was a FL resident and the Trust was created in Florida upon their death. However, the trustees and beneficiaries are all in Illinois. I'm thinking it's now an Illinois trust, but I'm not as familiar with Trusts as others in my office. Any pointers on where I should be looking or considering in trying to reach a conclusion?