Wendy- was at Ballymena Library today looking at 1901 Census and took a quick look at Protestant St. for Thompson- found them!
Robert Thompson's age was given as 76 (could it be his marriage in 1849 to Ellen Livingston?) and a gardener.
Rachel Thompson was 50 (26 years younger tham her husband).
Daughter Mary Ann was 16 and a weaver.
Their religion is down as Episcopalian, which would be Church of Ireland.
Also in the household were an Elizabeth Brown (25) married and her children- Margaret 5 (b/Co.Down), Marie 2 (b.Co.Down) & Rachael 4 months (b.Co.Derry).
Could Elizabeth Brown be Elizabeth Thompson, born 15 Nov.1871, daughter of Robert & Rachel?
If you want me to send you a photocopy of the census entry send me a PM with your mailing address.