Original OS maps at the Ordnance Survey of Ireland website.
(Click on place name to view original map in new window.)
This link is not a link to the townland that you are currently researching; however, if you follow this link, you will see a search box near the top of the page which you can use to search for your townland.
Having followed this link, you will see several expandable links - each link has a plus sign on its left - on the top left of the page. Expand 'Base Information and Mapping'. Now it is possible to select the maps that you wish to view by clicking on the checkbox that is on the left of each map; this list includes the original Ordnance Survey maps.
You can select more than one map and you can use a slider to make one map more transparent than another. This allows you to view what features were present or absent at different points in time.
(This map will display in a new window.)