county, north-central Vermont, U.S. Its topography is mountainous, with the main ridge of the Green Mountains traversing the western part of the county. The region contains some of the state's highest mountains—including the Sterling Range and Hogback, Cold Hollow, and Lowell mountains—and is forested with spruce, fir, hard maple, white pine, and hemlock. The county, created in 1835, is named for its principal waterway, the Lamoille River. Its tributaries are the Wild Branch and Gihon rivers as well as the Green River, which is impounded at the Green River Reservoir. Other lakes include South Pond and Lakes Elmore and Eden. The county features more than a dozen covered bridges. The Long Trail follows the crest line of the Green Mountains, while parklands include Elmore and Smugglers Notch state parks, Morrisville Village Forest, and parts of Mount Mansfield and Putnam state forests.

In the mid-20th century, tourism joined agriculture and lumbering as a major economic activity. Resort villages such as Stowe support popular skiing facilities. Hyde Park is the county seat. Other villages are Morrisville, Cambridge, and Johnson. Area 461 square miles (1,193 square km). Pop. (2000) 23,233; (2007 est.) 24,676.