unfortunately the oldest surviving census of Ireland is 1901..
the familysearch index I mentioned earlier seems to be down for maintenance at the moment, but it is worth checking this.
To start a search of parish records you need to know the religion and location (parish or townland). Some parish record transcripts are available on the Irish Family History Foundation website but Co. Wexford is not included at the moment. RC records are available on microfilm in the National Library (
www.nli.ie) and many Church of Ireland records are available at the Representative Church Body in Rathfarnham (
www.ireland.anglican.org)
not sure if this would be on any use ... but there is the 'census substitute' Griffiths Valuation which was carried out in the 1850s and includes heads of households. This was a land taxation survey - a (free) version can be found here :
http://griffiths.askaboutireland.ie/gv4/gv_start.phpsorry no idea on the GPV notation - where on the page is this written ?
Shane