File is a safe, fast, and easy way to file your tax return. Learn how to pay your income taxes.Information on how to file business and fiduciary income taxes with the city of Detroit. If you selected to file Detroit, it would have filed as part of the MI return. The Detroit return is just one of the forms in the state return. A PDFfillable copy can be found here. After filling it out, download it to your computer, then attach it here. Visit the Detroit city tax office in person. Obtain tax forms and assistance from staff. Who Must file Detroit tax return?