Hi, Jane. I was trolling through some old, old posts on the message boards this week, and I came across your inquiry from about 12 years ago about William McConnell.
I have a William McConnell in my line. He was born 1793 in Ballynahatty, County Down. His father was Andrew McConnell (1764-1833) and his mother was Mary Brindley (1760-1846). He had four siblings: Elizabeth (married McMullen), Margaret (married Thompson), James (married Smith), and John (married Martin).
It is thought that our William married Mabel Cook, but I have no supporting documentation for that, so it could be wrong. Maybe your Isabelle is the correct spouse. We also think he emigrated to USA and settled in Cicero, Onondaga County, New York, between 1810 and 1820.
Elizabeth, Margaret, and John all stayed in the Ballynahatty and Lisburn (Lisnastrean) areas and raised families. James emigrated to USA in 1811 and settled in New York and then Springfield, Illinois.
Let me know if you'd like to exchange information about this family.