Addison County was established by act of the Legislature October 18, 1785,[3] during the period of Vermont Republic.

[citation needed] The Champlain Canal was opened in 1823, making it possible for ships to navigate from the Hudson River.

[citation needed] In 2008, the federal government declared the county a disaster area after severe storms and flooding June 14–17.

[12] In terms of ancestry, 18.1% were English, 17.2% were Irish, 12.0% were German, 7.5% were American, 7.2% were French Canadian, 5.9% were Italian, and 5.3% were Scottish.

[15] In 1828, the county voted for National Republican Party candidate John Quincy Adams.

From William Henry Harrison in 1836 to Winfield Scott in 1852, the state would vote the Whig Party candidates.

From John C. Frémont in 1856 to Richard Nixon in 1960, the Republican Party would have a 104-year winning streak in the county.

Following the Democrats victory in 1964, the county went back to voting for Republican candidates for another 16 year winning streak starting with Richard Nixon in 1968 and ending with Ronald Reagan in 1984, who became the last Republican presidential candidate to win the county.

Public bus service in Addison County is operated by Tri-Valley Transit (formerly ACTR).

There is extensive bus service around Middlebury with connections to Vergennes, New Haven and Bristol, seasonal service to Middlebury Snow Bowl, as well as commuter buses to Burlington and Rutland operated in conjunction with Green Mountain Transit and the Marble Valley Regional Transit District, respectively.

This system enhances ACTR's ability to provide comprehensive transportation alternatives for all Addison County residents.

[20] Amtrak's daily Ethan Allen Express train serves two stations in Addison County: Middlebury and Ferrisburgh–Vergennes.

The train makes major stops in Burlington, Rutland, Albany, and New York City.

Begun in July 2022, this is the first regular passenger rail route in the county since the Rutland Railroad discontinued service in 1953.

[21] Vermont Translines, an intercity bus carrier and interline partner with Greyhound and Amtrak, serves Addison County from Middlebury and Vergennes as well.