The Dearborn's clarity impressed Meriwether Lewis, and he made this observation after a brief exploratory trip on July 18, 1805: "At the distance to 2.5 miles we passed the entrance of a considerable river on the Stard.
The highly picturesque Dearborn gets its start high on Scapegoat Mountain near the Bob Marshall Wilderness, and it carves a deep and beautiful path as it winds its way out of the mountains and onto the open country that once was the buffalo hunting grounds of the Blackfeet Indians.
Although the Dearborn is rather small, it's a high-quality stream with a floatable distance of 45 miles.
Geographically, Dearborn County is a mixture of flatlands in the northwest and rolling hills divided by several creeks forming long valleys throughout the county.
The principle waterways are the Whitewater River in the northwest corner of the county, the east and west forks of Tanners Creek, North and South Hogan Creeks, and Laughery Creek.
The population of Dearborn County grew from 4,424 in 1815 to 23,000 by 1890.