Ballymore Cobh A.C. 231, Midleton A.C. 203, Eagle A.C. 203, St. Finbarrs A.C. 188, Ballintotis Fit4Life 176, Bandon A.C. 172, Leevale A.C. 172, Mallow A.C. 148, Youghal A.C. 132, Watergrasshill A.C. 119, Togher A.C. 110, Clonakilty Road Runners A.C. 86, Tracton A.C. 83, North Cork A.C. 82, Rosscarbery Steam Runners A.C. 70, Bantry A.C. 67, Grange/Fermoy A.C. 66, Galtee Runners A.C. 66, Carraig-Na-Bhfear A.C. 65, St. Catherines (Cork) A.C. 54
It's probably worth mentioning as well that this doesn't represent the full story as one of the biggest growth areas in recent times has been that of running groups who are not members of athletics Ireland. There are now a number of these throughout the county and some are quiet large. e.g. Wibbly Wobbly Wonders in Ballyvolane, Happy Feet in Blarney, etc.
The latest stats from Athletics Ireland can be found HERE