Yes. He was a slave owner the day he died.
I know he held a position as a teacher at a military school in Virginia (I believe that school was a predecssor to VMI). I was not aware that he even owned any land or a plantation.
Most slave owners didn't own plantations. Slavery was very much a middle-class institution and most slaves didn't work in the fields. They worked in the houses as maids, cooks, gardeners, grooms, what have you. The number of slaves that Jackson owned at any one time varied, but it was as many as seven or eight.
Would like to see some documentation for this claim. Quite possibly accurate for the state of VA, but not for the South as a whole.