Connecticut State Income taxes can be prepared and e-filed using IRS Federal Tax return forms by the taxpayer using Tax2efile. A resident of Connecticut is someone who lived in Connecticut during the entire taxable year and spent a total of more than 183 days during the taxable year. You must have your W2 Form in order to fill the tax return. Tax2efile is used to file your state tax by using an easy e-filing process. Form CT-1040 needs to be filed on or before April 15th each tax year. If the due date falls on a Saturday, Sunday, or federal holiday, the due date is moved to the next business day.