The first white men to enter the county were French and British fur traders. Efforts were made to set up trading posts on the Leaf Lakes and Otter Tail Lake. In the late 19th century, most of the towns were built along the railroad lines. Lumber and agriculture were the major industries in the county at that time. The pine and hardwood forests, transportation system, and markets were instrumental in the development of Fergus Falls into a lumber center. The Wisconsin Territory was established by the federal government effective July 3, 1836, and existed until its eastern portion was granted statehood (as Wisconsin) in 1848. The federal government set up the Minnesota Territory effective March 3, 1849. The newly organized territorial legislature created nine counties across the territory in October of that year. One of those original counties, Dakota, had a section partitioned off in 1851 to create Cass County. On March 18, 1858, the outgoing territorial legislature created Otter Tail County from areas partitioned from Cass and Pembina, another of the original counties created in 1849. The county was named for Otter Tail Lake and the Otter Tail River. The county was not organized in 1858, nor was a county seat specified. On September 12, 1868, the legislature completed the county organization, and specified Otter Tail City as county seat.