Strengthen the Earned Income Tax Credit Act of 2011

Strengthen the Earned Income Tax Credit Act of 2011 - Amends the Internal Revenue Code to: (1) make permanent the reduction in the marriage penalty applicable to the earned income tax credit, (2) increase such tax credit for families with three or more qualifying children and for individuals with no qualifying children, (3) extend such credit to individuals at age 21 (currently age 25) who do not have a qualifying child, (4) allow such credit for certain married individuals who live apart from their spouses and file separate tax returns (abandoned spouse rule), (5) repeal provisions denying such credit for individuals with excessive investment income, and (6) increase to $500 the penalty on tax return preparers for failure to be diligent in determining eligibility for the earned income tax credit.

Makes permanent provisions of the Economic Growth and Tax Relief Reconciliation Act of 2001 relating to the earned income tax credit.