Part-year residents of PA must file PA personal income tax returns, filling in the oval for a part-year return and recording the time they were residents. Most states will consider you a resident for tax purposes if you spend 183 days or more in that state.Form 6166 is a letter printed on US Department of Treasury stationery certifying that the individuals or entities listed are residents of the United States. Your domicile is your fixed and permanent home to which you always have the intention of returning whenever absent, even though you may live elsewhere. There are several possible tax advantages to establishing Florida as your legal residence, including income taxes, property taxes, and state death taxes.