Exhibit 21 List of Subsidiaries of State Auto Financial Corporation Exhibit 21 List of Subsidiaries of State Auto Financial Corporation State Auto Property and Casualty Insurance Company, a South Carolina corporation State Auto National Insurance Company, an Ohio corporation Stateco Financial Services, Inc., an Ohio corporation Strategic Insurance Software, Inc., an Ohio corporation Milbank Insurance Company, a South Dakota corporation Farmers Casualty Insurance Company, an Iowa corporation Mid-Plains Insurance Company, an Iowa corporation State Auto Insurance Company of Ohio (formerly known as State Auto Insurance Company), an Ohio corporation 518 Property Management and Leasing, LLC, an Ohio limited liability company