Actually, those are the ARMS of County Antrim, not it's crest. While I will not profess to know everything about Irish civic heraldry, to the best of my recollection no county in Ireland (North or South of the border) has what could be properly deemed a crest.

Although many Irish identify with their County, the decision was taken to offer only two generic Irish cap badges: the harp and the shamrock. As others have pointed out Gaelic Themes does produce Irish clan badges for some of the more common Irish surnames.