Cullman County is a county located in the north central portion of the U.S. state of Alabama. As of the 2020 census, the population was 87,866. Its county seat and largest city is Cullman. Its name is in honor of Colonel John G. Cullmann.

Cullman County comprises the Cullman, AL Micropolitan Statistical Area, which is a component of the Birmingham-Hoover-Talladega, AL Combined Statistical Area.

It is served by TV stations and FM radio stations from both Huntsville and Birmingham and is part of the designated market area, or "DMA," of Birmingham. Cullman is a "moist" county in terms of availability of alcoholic beverages; the cities of Cullman, Good Hope, and Hanceville allow sale of alcohol and are "wet" and the rest of the county is dry.

This area was inhabited for thousands of years by varying cultures of indigenous peoples. The historic Cherokee and Choctaw lived here at the time of European encounter, with the Cherokee moving in after the American Revolutionary War and in response to pressures from northern areas. Their settlements in Alabama were known as the Lower Towns.

People claiming descent from Cherokee who remained in the county after Indian Removal in the 1830s, organized as the "Echota Cherokee Tribe of Alabama" in the 1980s. The tribe was recognized by the state in 1984 but is not federally recognized. It claims 22,000 members in the state, mostly in northern Alabama.

Cullman County was organized on January 24, 1877 from Blount, Morgan, and Winston counties. The act of establishment named March 6, 1877, as the day that residents would select the location of their county seat. The election pitted two towns, Cullman and Milner against each other. In the March 1877 election, Cullman defeated its rival and became the county seat, 760 votes to 55.

The county was organized by primarily by German American immigrants who had moved down from Cincinnati, Ohio. They founded an agricultural community and sought to create an agricultural revolution in what had been a frontier area, in the best traditions of innovation in the New South. However, hard geographical and social realities clashed with the often impractical vision of colonizer John G. Cullmann. His Germans, with their traditional work ethic and willingness to experiment with such new products as wine and strawberries, tried to make practical changes in southern farming. The Germans were outnumbered by more traditional families from neighboring regions, who replicated the traditional southern cotton culture.

On April 27, 2011, Cullman was hit by the 2011 Cullman tornado, which took place during the 2011 Super Outbreak.