Recently, the Irish Minister for Arts, Heritage and the Gaeltacht allowed all pre-1901 Irish census records to be released online.
You can find the census collection and other searchable Irish archives here. Unfortunately, the pre-1901 census records are not complete. Here's a little bit of information from the Irish Times:
True censuses were taken in Ireland every 10 years from 1821, a full two decades before anywhere else in what was then the United Kingdom.
By the time the 1911 census had been completed, there were full sets of no fewer than eight censuses in existence, the earliest four transferred to the Public Record Office, the others still held by the Office of the Registrar-General, the body responsible for census-taking after 1851.
Then things started to go horribly wrong.
First, at some point during the first World War, the Registrar-General ordered the 1881 and 1891 returns to be pulped, for reasons that are still murky. (The 1861 and 1871 returns had already been destroyed, shortly after the censuses were taken, again for reasons that remain unclear.)
And then, of course, in June 1922 the Public Record Office was destroyed and every single item held in its Strong Room, including the four earliest censuses, was obliterated without trace.
All that survived of them were the few bits and pieces that happened to be in use in the reading room or out for conservation: 29 parishes in Galway, Offaly and Meath (1821); 42 parishes in Derry (1831); part of Killeshandra (1841); parts of 14 parishes in Antrim (1851).So you can't search for census records for all of Ireland but it's still a great collection to have digitized and searchable (for free!) online. The National Archives of Ireland have a lot of other resources on their website to help with your Irish genealogy.