A Quick answer, I only looked for Shields and learnt there are many spelling variation, the Gallagher have the same spelling variants and are probably in each of these records
from Hearth money rolls see
http://www.billmacafee.com1660’s
Donegal Inishowen East Clonmany Clehagh Cleagh Torlagh o'Sheale Shiels
Donegal Inishowen East Clonmany Clehagh Cleagh James o'Sheale Shiels
Donegal Inishowen East Culdaff Aghaglassan Aghiglashan Bryan o'Sheale Shiels
Donegal Inishowen West Fahan Lower Meenagory Monegory Cu'mon o'Sheale Shiels
Donegal Raphoe Kilteevoge Ballykergan Ballykerigan Donell o'Sheale Shiels
Donegal Raphoe Raphoe Figart Figert James Shiels Shiels
1796 Flaxgrowers of Ireland
Sheal Arthur Tullyaughnish Donegal
Sheal Denis Clondavaddog Donegal
Sheal John Clondavaddog Donegal
Sheal John Conwal Donegal
Sheal Wm. Tullyaughnish Donegal
Sheals Cain Kilmacrenan Donegal
Sheals Camack Clonmany Donegal
Sheals Daniel Donaghmore Donegal
Sheals Dennis Clondavaddog Donegal
Sheals Edward All Saints Donegal
Sheals Edward Tully Donegal
Sheals George Raphoe Donegal
Sheals John Clondavaddog Donegal
Sheals Michael Kilmacrenan Donegal
Sheals Roger Tullyaughnish Donegal
Sheals Rose Moville Upper Donegal
Sheals William Raphoe Donegal
Sheil James Clonmany Donegal
1828 Tithe Applotment Books
fromhttp://titheapplotmentbooks.nationalarchives.ie/
Sheilds Jas Grillagh Clonca Donegal 1828
Sheilds Michl Drung Clonca Donegal 1828
Sheilds Michl Ballycramsy Clonca Donegal 1828
1857 Griffiths Valuation did I look at variant spellings
1857 Shields Catherine Main Street, Glenties Inishkeel Donegal
which is in GORTNAMUCKLAGH townland
Good luck onwards