Continuing to access Ancestry.co.uk, my next four searches looked as if they might be related. They were for McIlhagar, M'Ilhagar, McIlhaggar and M'Ilhaggar. McIlhagar gave me two marriages, registered at Ballymena, both of which I recognised, namely:
Eliza, 1847, Vol.2 p.60, spouse Robert McCarley;
Mary, 1847, Vol.2 p.63, spouse John Auld.
I recognised both were from the Broughshane area where my own family came from. Both were married at Broughshane 1st Presbyterian Church. However, I have not been able to put either in a family tree. This fact sent me back to look at the tree which was geographically nearest to my own, the one based at Newtowncromelin (just north of Broughshane) and on which I had made a note that one set of siblings were probably in the wrong place as there was obviously a two generation gap to their 'parents'. This made me write down, with dates, all the people I knew about from the area (the civil parish of Skerry) and then group them in generations, making the assumption (right or wrong) that they would have a common ancestor (whom I called Generation 1). Here is how it panned out (all fairly speculative at this stage, but sometimes you have to speculate!):
Generation 1: An Unknown McIlhagga, probably born about 1750.
James (born about 1780) who might have married a Sarah or a Margaret.
John (born 1788) who married Jenny McCarley (born about 1790).
[Possibly Samuel (b.1780) and William (b.1782) on Island Magee. If these are included the Unknown of Generation 1 would be their father James].
Generation 3: Four men who could be offspring of the Generation 2 James:
James (born about 1800);
William (born about 1807) who married Agnes McCosh, parents of William (b. 1829) who married Elizabeth Carson in 1851 (and who may have been witnesses at the Auld wedding - see below);
John (born about 1810), possibly the father of Elizabeth (1830), Martha (1833), Robert (1835) and James (1836). See Generation 4 below for these.
Crawford (born about 1812, who married Martha and had a daughter Margaret (b.1833) who married John Hill.
Generation 3: Three children who could be the offspring of John McIlhagga and Jenny McCarley of
William (b.1800), father of Mary (b.1825) who married John Auld in 1847;
Elizabeth (who may have been born in Kent in 1808 to a Soldier then known as John McHagga);
David (born 1806) who married Mary and had four children.
William (b.1829) daur of William & Agnes, who married Elizabeth Carson;
Elizabeth (b.1830) daur of John, who married Robert Graham in 1851;
Martha (b.1833) daur of John, who married James McCrory
Robert (b. 1835) son of John, who married Mary McAteer in 1849 and had a daughter Mary Jane;
James (b.1836) son of John, who married Eliza [Rogers] and had 5 children.
Margaret (b.1833) daur of Crawford & Martha, who married John Hill and had seven children (1855-1877);
Mary (b.1825), daur of William, who married John Auld in 1847;
Eliza (b.1828), daur of Eliza(beth), who married Robert McCarley in 1847;
Isabel (b.1835), daur of David and Mary, who married Henry Fortney and had a son James Henry in 1863;
John (b. 1840, d. 1841) son of David and Mary;
John (b. 1845) son of David and Mary;
George (b. 1849) son of David and Mary.
I am offering this analysis simply as a working hypothesis for the clan relationships in the Civil Parish of Skerry, in the Broughshane and Newtowncromelin area of County Antrim. I will continue to look at M'Ilhagar, McIlhaggar and M'Ilhaggar next time.