Another source I almost forgot: The city of Vergennes has tax grand lists going back to the 1860s or earlier. These list all taxpayers in the city. In addition to property taxes, people had to pay poll taxes (if they were U.S. citizens) and could be charged for other things, such as owning a dog. If you get up to Vergennes, stop at the City Clerk's office. The grand lists are in the vault with the land and vital records. (I'm at my office now; when I get home, I will check the photocopies I made of Januarys. The Jenners, if there are any those years, are probably on the same page.)
As for the 1900 census, Peter and Julia Jenners and a daughter named Hazel(?sp) are listed on page 5B of Enumeration District 22 for Addison County. (To see the image on Ancestry, click on 1900 census, then browse Vermont, then Addison County, then Vergennes city, then go to image number 10.) They are near the bottom of the page. Are these your people?