Head of Household doe not require legal separation, only physical separation.
Head of Household is for UNMARRIED taxpayers with a related dependent or married and have not lived with their spouse at anytime during the last 6 months of the tax year AND has a child, stepchild or foster child that can be a dependent.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**