Kornegay is a common American surname of German origin, coming from the German Kornegger, from the Middle High German korn, meaning 'grain', and acker, meaning 'field'; it was used, unsurprisingly, for someone living by a cornfield. It is perhaps worth noting that at this place and time, korm would have referred to wheat, rye, or barley, not maize.
The name Kornegay is most common, in the United States, in the American South and along the East Coast, with the greatest concentration in North Carolina. This seems to be due almost entirely to the emigration of John George Kornegay Sr, who was born in 1701 in Upper Palatine, Rhein River, Germany. He died in 1773 after moving his family to Craven, NC. Despite this origin, the name is currently shared fairly evenly between European American and African American families. It is pronounced either korn-a-gay or kor-nig-gy.