Hennepin County (/ˈhɛnəpɪn/ HEN-ə-pin) is a county in the U.S. state of Minnesota. As of the 2020 census, the population was 1,281,565, and was estimated to be 1,273,334 in 2024, making it the most populous county in Minnesota and the 34th-most populous county in the United States. Its county seat is Minneapolis, the most populous city in Minnesota and the 46th-most populous city in the United States. The county is named for the 17th-century explorer Louis Hennepin. It extends from Minneapolis to the suburbs and outlying cities in the western part of the county. Its natural areas are covered by extensive woods, hills, and lakes. It contains over 21.98% of the state's population. It is included in the Minneapolis–Saint Paul–Bloomington metropolitan statistical area.

The Territorial Legislature of Minnesota established Hennepin County on March 6, 1852, and two years later Minneapolis was named the county seat. Louis Hennepin's name was chosen because he originally named Saint Anthony Falls and recorded some of the earliest accounts of the area for the Western world. In January 1855, the first bridge over the Mississippi River was built over St. Anthony Falls.

Waterpower built the city of Minneapolis and Hennepin County. The water of streams and rivers provided power to grist mills and sawmills throughout the county. By the late 1860s, more than a dozen mills were churning out lumber near St. Anthony Falls and the county's population had surpassed 12,000.

In many ways, the falls' power was the vital link between the central city and the farmsteads throughout the county. Farms produced vegetables, fruits, grains and dairy products for city dwellers, while Minneapolis industries produced lumber, furniture, farm implements and clothing.

By 1883, railroads united Minneapolis with both the East and West coasts, and technical developments, especially in flour milling, brought rapid progress to the area. The major Minneapolis millers were Washburn, Pillsbury, Bell, Dunwoody and Crosby. For a decade, the "Mill City" was the flour-milling capital of the world and one of the largest lumber producers. Minneapolis, with a population of 165,000 by 1890, had become a major American city, and by 1900, was firmly established as the hub of the Upper Midwest's industry and commerce.

Hennepin County's farm economy was also substantial. In 1910, farmland in the county totaled 284,000 acres, about 72% of its area. The principal crops were wheat, corn, garden vegetables, and apples. The number of acres in production remained high for the next 30 years. By 1950, the amount of land devoted to agriculture had declined to 132,000 acres as development progressed in the suburbs.

During the 1950s and 1960s, many suburbs grew rapidly as housing developments, shopping centers, large school systems and growing industrialization replaced much of the open farmland. By 1970, Hennepin County's suburban population outnumbered the cities for the first time. Minneapolis's population declined by 10 percent from 1960 to 1970, while the suburban population grew by nearly 50 percent.

Another wave of immigration—which began after the Vietnam War in the mid-1970s—marked a major change in the county's ethnic makeup. This wave peaked in the 1980s when hundreds of refugees from Southeast Asia, often aided by local churches, resettled in Hennepin County. Its population surpassed one million in 1989.