The 1901 census data was collected from areas defined as District Electoral Divisions, and this set of data follows that pattern. Some researchers have submitted townlands based on the civil parish, without the DED, and these are indexed by civil parish. So be sure to check both indexes when you are looking for your townland. A few townlands are duplicated in both sets of organization.

Read more about DEDs at wikipedia.

As of November, 2011, the 1901 and 1911 censuses are published online at The National Archives of Ireland.