The
Eighteenth Century Sources. may assist you to find your Nelson ancestors of Gortnamoyagh. Some of them are on John Hayes failteromhat.com website
Books of Survey and Distributions c. 1700
Catholic Qualification Rolls 1778 - 1793
Convert Rolls 1704-1839
Electors Rolls 1761
Estate Records and Marriage Licence Bonds
Flax Growers List 1796
Freeholders entitled to vote 1770
Grand Jurors and Books of Presentiments
Militia Lists 1761
Oath of Allegiance 1775
Poll Books 1752
Proprietors of land circa 1700 list
Protestant Householders 1740 list.
Register of Freeholders 1758
Return of Householders 1766
State prisoners 1798
Voters Lists 1727-1793
The 1796 Flax Growers List shows one Nelson in Derry ... Hugh, Ballywillin. Other Nelson families on the list were in Donegal, Down, Fermanagh, Mayo, Monaghan and Tyrone.
I've created links to the following threads ...
Rootsweb "Johnston & Nelson of Gortnamoyagh" ...
http://tiny.cc/9Kt3k Jane Agnes Dobbins on Rootschat
http://tiny.cc/OLbth Neilson/Nelson & Johnston's from Garvagh-Aghadowey
http://tiny.cc/uqUS0 Christopher