Mississippi taxes ordinary income at 0%β5%. Roth conversions are treated as ordinary income, so a large conversion adds to your MS state tax bill in the year you convert. At the top state rate of 5.0%, a $250K conversion costs $12,500 in state tax alone.
Mississippi exempts retirement income (401k, IRA, pension distributions) from state income tax. This changes the Roth calculus: if you convert now, you pay state tax; if you leave funds in a traditional IRA, future withdrawals may also be exempt. Run the numbers on whether a conversion still makes sense given this exemption. It often still does for federal tax reasons, but the state advantage of Roth narrows.