The following were head of households in 1831Killowen Killowen [part of Coleraine] Elizabeth CummingAghanloo Ballycarton George CumminsMagilligan Ballymaclary Thomas CumminsMagilligan Carnowry John CumminsMagilligan Oughtymoyle Patrick CumingMagilligan Tircreven David CummingMagilligan Tircreven Henry CummingMagilligan Tircreven Samuel Cumming jnrTemplemore Ballyarnet Joseph Cummins
Microfilm of the 1831 census is in PRONI, NAI [and Ballymena Library].
perhaps the clergyman wrote his own interpretation of the name in the register. This did happen quite frequently. Also could you try and search the ballykelly parish baptism register for children born of that union and see what way the clergyman spelt the name ? Working from that you can then try and see did any of those children marry in the parish or whom they married and keep working forward.Hope this helps.