Sorry, Diane, but with as little information as that there is absolutely no possibility of identifying your William Campbell. According to Scotland's People 606 William Campbells were born in Scotland in the 1860s.
I see from the Northern Ireland BMD web site that the marriage of William Campbell and Rachel Speer on 13 February 1906 was registered in Magherafelt, Reference M/1906/N1/1855/6/27. Your first step is to go to
https://geni.nidirect.gov.uk/ and buy a few credits, then download the marriage certificate. This will tell you the name and occupation of William Campbell's father.
From the same site I see that their children may have included
Violet, born 24 August 1906
Margaret, born 19 March 1908
Mary, born 4 January 1909
Dawson, born 21 September 1910
Agnes, born 12 July 1914
all registered in Magherafelt except Violet, but you'd need to check the certificates to be certain. Also, the site does not include children born less than 100 years ago.
The original 1911 census lists at House 33 in Drumenagh, Ballyronan, Londonderry
William Campbell, 50, agricultural labourer,
born County DerryRachel Campbell, 36, born County Derry, married 5 years, 3 children, 2 living, 1 dead
Mary Ann Campbell, 2, born County Derry
Dawson Campbell, 6 months, born County Derry
Isabella Griffan, 80, boarder, widow, born County Derry
All were protestants.
Margaret Campbell, aged 0, died on 19 April 1908, death registered in Magherafelt. Given that Rachel had had three children, one of whom had died before 1911, it looks as if Margaret had died, and also that Violet has nothing do do with this family.
Why do you think that William Campbell was born in Scotland, when the 1911 census says that he was born in County Derry?