Bruce,looked through various records and found the following:
Births: Jane Laird b 22 Sept 1871 Toronto,York,Ontario Sarah Laird b 11 Nov 1874 Halton,Ontario Henrietta Louisa Laird b 13 Jan 1880 Halton,Ontario Margaret Ann Laird b 1 Aug 1881 Halton,Ontario William Laird b 10 Feb 1884 Halton,Ontario Ida Winnifred Laird b 11 Oct 1886 Halton,Ontario I couldn't locate Samuel's birth.
according to census records both Sarah Donaldson's mother and father were born in Ireland but Samuel Laird's father was born in Ireland and his mother was born in Scotland.
for Samuel Laird found 4 birth records all in county Donegal;1830,1838,1844,1850 for Sarah Donaldson between 1845-1865 I found 10; co Down 1852,1865 co Derry 1846,1860 co Donegal 1863 co Antrim 1846,1865 co Sligo 1854 co Kilkenny 1847,1853
the marriage between Samuel Laird and Sarah Donaldson took place in co Armagh in 1871
looked at Irish Royal Constabulary records and found 2 Samuel Lairds as having enlisted one in 1878(which is too late for your relation).The other Samuel enlisted in 1855 age 19 born in co Derry.Its film # 856061.
If you go back to the birth records and see that all the Samuels I could find were born co Donegal its very possible that he was born in co Derry and the birth registered in co Donegal as co Derry(and city of Derry)border co Donegal. To get the marriage record for Samuel and Sarah or any birth records, these are available on rootsireland.ie.The births of the children as well as other records concerning the children (such as the onee below)can be found on familysearch.org.
Ida W Dancey age 27 born 1887 Actan,Ontario married Albert Rosa born in Clinton county,Missouri on 18 Aug 1914 in Cuyahoga,Ohio bride's parents:Samuel Laird/Sarah Donaldson groom's parents:Edward Rosa/Rebecca Swearingen bride's former husband's name:Dancy