Harry first produced a Patronus when he was practicing against a Boggart with Professer Lupin, although that wasn't a corporeal Patronus (a Patronus with a shape). It was more like wisps of silvery smoke or fog, really.
Harry's first corporeal Patronus was produced when he and Hermione went back in time to save Sirius and Buckbeak
who destroyed the Salazar Slytherin Locket and how (from which)?
