Julie, I don't know William was born there. Only that he was there in 1866 since James Robert was born there. So it is possible in the 6 years since the census another Will Sullivan moved to the county. I have found 2 seperate Mary Adams in the county who were close to Williams age. I have yet to find a marriage certificate. I have only recently started searching and have not yet made a trip there. I have entertained the thought that perhaps they never actually married. The William in the census would have been 25 in 1866, so a very appropriate age. As you well know the Sullivans are a challenge to track down :)