Yes. You can claim your ex-spouse as a dependent if her gross income is less than $4,050 for the year (SS income is not included) and if you provided more than half of their total support, and they lived with you for the entire year.
However, your ex-spouse, even if claimed as your dependent, does not qualify you for Head Of Household. You must have a qualifying child, parent or relative as a dependent. A non-relative does not qualify. If you don't otherwise qualify as Head of Household, you'll file Single, not Married.
