Dewey Township was originally part of Van Buren Township in Starke County. When a section of Starke County was ceded to LaPorte County in 1842 what was to become Dewey Township was included within the Cass Township boundaries. In 1860, Dewey was organized as a separate township and was named for the Dewey family who were early settlers.
The Kankakee River, which forms the township’s southern boundary, contributed to large expanses of marshland. Almost one-half of the township’s area flooded every spring. Because of these conditions and because much of the township was owned by land speculators, settlement was slow.
The first settler was George Schimmel who came to the area in 1854. Four years later the township’s first school was built on Hog Island. Most of the early settlers were Germans who produced hay and kept stock farms, two of the township’s leading industries.
New construction in 1852 of the Louisville, New Albany and Chicago Railroad through the township was followed by four other rail lines within the next few decades. Four of those lines joined at a small town known as LaCrosse, the township’s only surviving town.