Hi,
The first complete extant census of Ireland is 1901. Others were either pulped in WW1 or lost in the Four Courts fire in Dublin in 1922. Some scraps of others do exist and the 1831 for County Londonderry is almost complete. Also when the Old Age pension was introduced in 1909 people had to prove that they were at least 70. One way was to quote the 1851 or 1841 census and the civil servants would note the details which usually included the whole family. However, except for the Londonderry and small Co. Cavan bits, I am not aware of anywhere where the rest are indexed.
Regards