Land-grant universities should host the state extension services that conduct and support the master gardener programs in the U.S. Also listed are some Canadian sites.
Alabama
Alabama Cooperative Extension System - Home and Garden Page
Alaska
Alaska Master Gardener
Arizona
Arizona Cooperative Extension Unit
Arkansas
University of Arkansas Division of Agriculture Extension Page
Arkansas Master Gardener
California
University of California Agricultural and Natural Resources Master Gardener Page
Colorado
Colorado State University Extension
Colorado Master Gardener
Connecticut
Connecticut Master Gardener
Delaware
University of Delaware Cooperative Extension Service
Delaware Master Gardeners
Florida
University of Florida Master Gardener website
Georgia
University of Georgia Cooperative Extension Service
Georgia Master Gardener
Hawaii
University of Hawaii Cooperative Extension Service
Hawaii Master Gardener
Idaho
University of Idaho Cooperative Extension Service
Idaho Master Gardener
Illinois
University of Illinois Extension
Indiana
Purdue University Horticulture and Landscape Page
Purdue Master Gardener Program
Iowa
Iowa State University Extension
Iowa State University Horticultural Department
Kansas
Kansas State University Extension Service
Kansas Master Gardener Program
Kentucky
University of Kentucky Extension Service
Louisiana
LSU Master Gardener Program
Maine
University of Maine Coop Extension Service
Maryland
U of Maryland Extension
Michigan
www.msue.msu.edu (Michigan State University Extension)
Minnesota
University of Minnesota Extension Service
Mississippi
Mississippi Master Gardeners
Missouri
University of Missouri extension service
Missouri Master Gardeners
Montana
Montana State University Extension Service
Montana Master Gardeners
Nebraska
University of Nebraska - Lincoln Extension Service
Nebraska Master Gardener Program
New Hampshire
The University of New Hampshire Cooperative Extension
New Jersey
Rutgers Agricultural Experimental Station - Cooperative Extension
New Jersey Master Gardeners
New Mexico
New Mexico State University Cooperative Extension
New Mexico Master Gardeners
New York
Cornell University Cooperative Extension Service
Cornell University Master Gardener Program
North Carolina
NC State Cooperative Extension Home Page
North Carolina Master Gardener Program
North Dakota
ND State Cooperative Extension Home Page
North Dakota Master Gardener Program
Ohio
Ohio State Cooperative Extension Service
Oklahoma
Oklahoma State University Cooperative Extension Service
Oklahoma Master Gardener Program
Oregon
http://extension.oregonstate.edu/gardening/ (Oregon State University Extension Service)
Pennsylvania
Penn State Cooperative Extension (Horticulture & Gardening)
South Carolina
http://hgic.clemson.edu (Clemson Extension)
South Carolina Midlands Master Gardener Association
South Dakota
SD State Cooperative Extension Home Page
South Dakota Master Gardener Program
Texas
Texas Master Gardener Association
Tennessee
Tennessee State University Cooperative Extension Program
Utah
Utah State University Extension
Utah Master Gardener
Vermont
University of Vermont Extension
University of Vermont Master Gardener
Virginia
http://www.ext.vt.edu (Virginia Cooperative Extension) - Connection to Virginia's land-grant universities: Virginia Tech and Virginia State University: local extension office, educational programs, and news.
Washington
Master Gardener Program (Washington State University Master Gardener Program)
West Virginia
http://www.wvu.edu/~agexten/hortcult/master/
Wisconsin
University of Wisconsin Cooperative Extension Program
Wyoming
University of Wyoming Cooperative Extension Program