Thank you very much for this information. It tells me that the Youngs stayed in Washtenaw Co, but that 'my' John Canavans either moved away, or weren't found by the census-taker, or had died before the 1850 census.
I have seen the records of the Kalamazoo area Canavans, and they arrived in the US later, and were not connected to the John Canavan who married in 1817.
I will continue my search, and thank you for your kindness. Patricia