From Historical Rutland : an illustrated history of Rutland, Vermont, from the granting of the charter in 1761 to 1911 by Rev. F. E. Davison, Rutland, Vt.: P.H. Brehmer, 1911, page 4:
Five Counties Carved Out of One
Not only so, but Rutland County has been carved out of at least five different counties since those early days. In 1683 Albany County embraced all the territory of the present county and much more. In March, 1778, Vermont was divided into two counties, Unity on the East side and Bennington on the west side of the Green Mountains. In 1770, the territory north of the present Bennington County and west of the mountains was given the name of Washington County. February 13, 1781, Rutland County was incorporated, embracing the territory Washington County had previously covered. So that Rutland County at that time extended from Bennington to Canada, and from the Green Mountains on the east to the Hudson River on the west, including within its confines Lake Champlain and Lake George. The population of the county at that time was a little more than 4,000 and the appraisal of property for taxation less than $100,000. The county seat was established at first at Tinmouth where it remained until 1784 when it was removed to Rutland. When Addison County was formed in 1784 Rutland County was brought to its present limits, with the exception of the loss of the town of Orwell, which was annexed to Addison County in 1847.
The territory of Rutland County during the Colonial and Indian wars was trodden by many hostile expeditions. It was subject to the depredations of both French and English armies at a later period and because of the dangerous conditions incident to the times, settlements were rare, and it was not untii after the complete conquest of Canada by the English in 1760 that any considerable move was made in the direction of populating this section of the country, a few points only having been occupied as military posts up to that time.