Possibly the swiftest route to your roots.
Irish genealogy website directory.
freepages.genealogy.rootsweb.ancestry.com/~donegal/lettertithe.htm
Description:
Tithes were an income tax on farming - usually about one tenth of the annual income. These were used for the upkeep of the Church of Ireland and were paid from the time of the Reformation. Before the Composition Act of 1823 it was possible to pay them in kind in stead of money.