There were no Cunninghams listed in Iderown in the 1803 Agricultural census, nor any in the 1827 tithes, so presumably they arrived in the townland after that. Or if they were there in the early 1800s it was as weavers and labourers, rather than as farmers. Nearest farmer in 1827 was John Cunningham of Lisnagatt.
http://www.irishgenealogyhub.com/antrim/tithe-applotments/derrykeighan-parish.php#.WNEM_RR2ug0
Griffiths shows William Cunningham on plot 2a in Iderown in 1861. The tenant changes to Robert in 1876 suggesting William died around then.
Family in 1901:
http://www.census.nationalarchives.ie/pages/1901/Antrim/Drumtullagh/Iderown/922822/
And in 1911:
http://www.census.nationalarchives.ie/pages/1911/Antrim/Drumtullagh/Iderown/114098/
I found this probate abstract. The file itself should be in PRONI in paper format:
Cunningham Robert of Iderone Stranocum county Antrim farmer died 18 June 1921 Administration (d.b.n.) Belfast 10 August to Mary Cunningham spinster. Unadministered effects £253. Former Grant Belfast 15 January 1923.
Cunningham Robert of Iderone Stranocuen county Antrim farmer died 18 June 1921 Administration Belfast 15 January to Eliza Ann Cunningham widow. Effects £268. D.B.N. BELFAST 10 AUGUST 1927
So Robert died intestate and the executors were twice unable to administer the estate for reasons beyond their control and it was 6 years after the death that it was finally wound up.
Presumably you know which church the Cunningham family attended? Have you checked the pre 1864 records for baptisms etc? Tradition was to marry in the bride’s church so the place that Wm Cunningham married Maria Cusack may not be the same church where their children were baptised. Cusack is not a common surname in Co. Antrim. And most of the Cusacks listed in the county in the 1901 census were RC. So this might have been a mixed marriage. In which case, in the 1830s, it may have taken place in the Church of Ireland as neither the RC nor Presbyterian churches would probably have married them. Unfortunately neither Grange of Drumtullagh nor Derrykeighan Church of Ireland has marriage records for the 1830s. Both sets were lost in the 1922 fire in Dublin.
A Mary Cunningham married Joseph Dallas on 30.9.1869 in Antrim town. Mary’s father was William according to the indexes I have looked at. Can’t say whether it’s your family but the marriage cert may tell you.
The couple had a son William James Dallas born at Shane’s Castle, Antrim on 21.5.1870. Joseph was a labourer.
Cunningham is a fairly common name in Co. Antrim. There were 771 in the county in the 1901 census. You might need DNA testing to identify others of your family there today. (Few families here would know their ancestry back to the early 1800s).