There is a history of Washington County on the VT Gen Web page. Briefly summarizing as follows: In 1787 Chittenden Co was formed and the western towns of what is now Washington Co were part of Addison and Chittenden Co's. Therefore Waterbury was considered part of Chittenden Co. until 1810/11 The text indicates that the name of Jefferson Co was changed to Washington Co. in 1814. ( However, Washington Co.is said to have been formed in 1810 (?) accoring to the web site).