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 is named for the people who inhabited it prior to European and American settlement, the Dakota. The eastern bands of Dakota had long-established villages at Black Dog (current day Burnsville) and Kaposia (South St. Paul) in Dakota County.

Some of the earliest immigrants to Dakota County were French-Canadian fur traders who established trade relationships with the Dakota well before Minnesota Territory was established. Later, Eagan and Mendota were largely settled by French-Canadians. Migration to Dakota County continued with people who left the eastern United States, often 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 including Poland, Romania, and Austria-Hungary (Croatia and Serbia) to work for the railroads or the packing houses in South St. Paul. The 20th century has seen immigration from Mexico, Laos, Somalia and many other countries in addition to migration from larger metropolitan areas around the country.

Dakota County, once almost exclusively agricultural, has become increasingly suburban over the past 60 years as its population exploded. In 1950, 49,019 people called Dakota County home, 50 years later the population of the County was 355,904 and still growing. While population growth has occurred county-wide, much of the suburbanization has occurred in northern Dakota County, particularly in Eagan, Apple Valley, Rosemount, Lakeville, and Burnsville. The net result is that Dakota County has lost a tremendous amount of agricultural land to residential neighborhoods, shopping centers, and industrial parks. Dakota County's inhabitants increasingly work outside the County as opposed to earlier generations who earned their living from the land.

The earliest European 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). The mill is the oldest continuously operating flour mill in the state of Minnesota, it was established in 1853. The one-time County Courthouse on Vermillion Street was sold to the City of Hastings and was restored and reopened as Hastings city hall in 1993.