Well, when it comes to it, I'm not entirely sure I write any OCs. Everyone seems to have a nominal place in the Potterverse. My only published main OCs are Suzanne Pallard, Cynthia Rookwood, Melania Frost, Catherine Black, Edmund Avery, and Jen Weasley.
But I mean, everyone else is basically an OC, no? With the exception of Severus Snape, Lucius Malfoy, the Crouches, and the other usual suspects.
Where does the line between minor character and OC lie? I think when written Cho Chang is a minor character, but Blaise Zabini is pretty much an OC.