Dakota County was established in 1849, one of the first counties in the new Territory of Minnesota. The western boundary of the county was the Missouri River, which is now halfway across the Dakotas. The county was named for the people who inhabited it prior to white settlement, the Dakota people. Some of the earliest immigrants to Dakota County were the French-Canadians who came to trade for furs with the Dakota people. Eagan and Mendota were largely settled by French-Canadians. Migration to Dakota County continued with people who left the eastern United States, or who were called Old Stock Americans, in the early to mid-1850s. In the latter part of the 19th century, immigrants came from Ireland, Germany, Norway, etc. By the late 19th and early 20th centuries people began to come from eastern European nations such as Poland, Romania, and Austria-Hungary (Croatia and Serbia) to work either for the railroads or for the packing houses in South St. Paul. The 20th century has seen immigration from Mexico, Laos and Somalia in addition to migration from the larger metropolitan areas.

Dakota County has lost a great deal of agricultural land to housing developments in cities such as Eagan, Apple Valley, and Burnsville. Dakota County has also lost agricultural land to industrial parks and has been threatened by a proposed airport in the Marshan area. More and more of Dakota County's inhabitants earn their living elsewhere and live in the county as opposed to earlier generations who earned their living from the land. The population of the county has increased dramatically from 8,556 in 1860 to 39,660 in 1940, to 335,904 in 2000.

The earliest settlement in Dakota County is Mendota, made possible by the establishment of Fort Snelling in 1819-1820. It is home to St. Peter's church, the oldest continuously operating stone church in the state of Minnesota, and the homes of Henry Hastings Sibley and Jean Baptiste Faribault, built in 1835 and 1839 respectively. The Mendota Bridge connects Mendota to Hennepin County and was the longest continuous concrete arch bridge in the world when it was completed in 1926.

The city of Hastings, established in the early 1850s, was originally called Oliver's Grove, and then Olive Grove, for the band of soldiers who wintered at the site during the winter of 1819-1820 under Lieutenant Oliver. Hastings has many National Register sites including two districts. One site which is not on the Register is the Vermillion Falls just south of the ConAgra Mill on Vermillion St. (Hwy. 61). This mill is the oldest continuously operating flour mill in the state of Minnesota, starting in 1853. The Hastings Courthouse on Vermillion has been restored and reopened as Hastings city hall.