Secular trends in Ireland

Although Catholicism is declining in both the north and the south, the situation is different in each country. The south is 84 percent Catholic, while the north is 48 percent. In both places, however, the number of those practicing their faith is significantly lower than those who just check the census box. According to Archbishop Diarmuid Martin of Dublin, in 1984, nearly 90 percent of Irish Catholics went to weekly Mass. In 2011, only 18 percent did. Numbers in the north are harder to come by. Rev. Edward McGee, spokesman for the Diocese of Down and Connor, where Belfast is located, said his jurisdiction has no longitudinal surveys on membership or attendance.
 

From here.