If you look through the baptism register, can you tell when the couple started and stopped having children? Most importantly right now, when they started?
Were they Protestant?
Protestant marriages were registered beginning in 1845, so if Protestant, you might find a civil marriage record.
Also, what about a parish marriage record, whatever denomination? How many William Wilsons married a "Mary"? If more than one, can you eliminate the others?
Did the baptism record list a townland - usually in the last column? That could help you id the father, assuming they settled in his townland, not hers.