Lake Lavon has 6500 acres of Corp of Engineers Land that is designated public hunting land. This is in Collin County which McKinney is also.
I have never hunted this area because it is very restrictive. Shotgun smoothbore with no shot larger than #2. But there are hogs there. And it is free.
Cannot post link because I don't have enough posts but it looks something like this lavonlakehunting_tamu_edu/policy