By the 15th day of the 5th month following the end of the taxable year. For most organizations, the tax year ends December 31 so the Form 990 is due May 15.File Attorney General Form PC, together with a copy of Form 990 or 990-EZ. Annual Filings for Massachusetts Nonprofit Organizations ; Form: Annual Return Form 990. Complete Parts VIII, IX, and X of Form 990. 5. Complete item G in the heading section of Form 990, on page 1. 6. Form 990 is an information return that most organizations claiming federal tax-exempt status must file yearly with the IRS. This Nonprofit Audit Guide provides links to the state laws that address audits so that you can determine what your state requires. Find 990 forms of private foundations, public charities, and other nonprofits. PO Box 8654. Pittsburgh.