Madison County is a county located in Idaho's Upper Snake River Valley. Named for James Madison, the fourth president of the United States, was established February 18, 1913 with the county seat at Rexburg. As of 2009 the population is 38,440. Madison County's first settlers were pioneer families from Utah, who built farms, roads, and the area's first irrigation system. This website provides a cost-effective way for our county to provide information and communicate with our constituents. We welcome your feedback about ways we can serve you better through these pages.