When the ice melted completely, the water from the lake ran out through the Lamoille River valley.

This area was long occupied by the Algonquian-speaking indigenous Abenaki people and their ancestors.

During French colonization of what is now Canada, fur traders began to trade with the Abenaki.

There were also French who settled here, coming down from the settlements in Quebec, and named the Lamoille River.

The French later enlisted the Abenaki as allies in the frontier raiding and wars with English colonists in the lower New England colonies.

In the United States, many of the French immigrants were forced to accept anglicization of their names, such as New City for Villeneuve, or Senton for St. Onge.

By the late 20th century, environmental hazards were better understood, but many of the miners contracted asbestosis and other diseases of the lungs from their work.

In 2008, the state notified residents of Belvidere, Eden, Hyde Park, Johnson, Waterville and eight towns in the adjacent counties of Orleans and Franklin, that a review of health records from 1995 to 2006 had revealed that residents within ten miles (16 km) of the former asbestos mine on Belvidere Mountain had higher than normal rates of contracting asbestosis.

[4] In April 2009 the Vermont Department of health released a revised study which found that all of deaths related to the asbestos mine were caused by individual occupational exposure.

As of the 2010 United States Census, there were 24,475 people, 10,014 households, and 6,274 families living in the county.

[dubious – discuss] In 1840 the county was won by Whig Party candidate William Henry Harrison.

In 1848 and 1852, the county was won by Free Soil Party candidates Martin Van Buren and John P. Hale, respectively.

In 1964, the county was won by Democratic Party incumbent President Lyndon B. Johnson.

Following the Democrat's victory in 1964, the county went back to voting for Republican candidates for another 20 year winning streak starting with Richard Nixon in 1968 and ending with George H. W. Bush in 1988, who became the last Republican presidential candidate to win the county.

The Community College of Vermont (CCV) is located in Morrisville in Lamoille County.