I would like to add to the information provided by Tom Coughlan (Leitrim expert and Dublin resident.
Discovery series road maps
Current Ordnance Survey road maps (approx. one inch to the mile), known as the "1:50.000 Discovery Series", includes most townland names but not the townland boundaries. The Discovery Series maps are readily available from specialist map retailers worldwide. They can be purchased on line from
www.gould.com.au or
www.irishmaps.ie
Your area of interest is on Discovery Series map 33. The grid reference for Drimna townland is 080 030.
For the complete index to the 1:50,000 Discovery Series maps see
http://www.irishmaps.ie/productlistingM.cfm?SeriesID=11
Have you seen the Mohill Civil parish map on the Leitrim-Roscommon website
http://www.leitrim-roscommon.com/MAPS/mohill.html
For more Mohill maps see visit
http://www.mohill.com/
Townland definition:
The Townland is the smallest administrative unit of land and varies in size. County Leitrim townlands vary in size from one acre (Crane Island) to 2805 acres (Slievenakilla townland. The average size is 246 acres. It is still the basic address used by rural Irish people for mail and telephone. Each Civil Parish is composed of a number of townlands. A town or village might comprise parts of a number of different townlands. Townlands can come in almost any shape, any size, and with all manner of names (eg. Gaelic, Norman, English, topographical). Note that many townlands in Co Leitrim share the same name. In Australia today we would refer to them as a "sub-division" or "an estate" that had been broken up into varying sized "lots" or "allotments" of land.
The spelling of townlands on the Resource County Leitrim CD is in accordance with the standard spelling listed in the “General Alphabetical Index to the Townlands, Parishes and Baronies of Ireland” based on the Census of Ireland for the year 1851. Currently in Ireland there is much debate about the spelling of townlands. The difficulty stems from the effort to spell townlands as they are pronounced. Often townlands are spelled incorrectly and the only reason that letters are delivered is because the postman knows were people live.
Historic maps
Ordnance Survey Ireland Mapping Archive now allows you to view and purchase the following Historic Maps online:
6 inch mapping series (1:10,560) colour 1837-1842
6 inch mapping series (1:10,560) greyscale 1837-1842
25 inch mapping series (1:2,500) greyscale 1888-1913
http://www.irishhistoricmaps.ie/historic/
John Hunter, Brisbane