Brown County is a county in the U.S. state of Nebraska. As of the 2020 census, the population was 2,903, and was estimated to be 2,826 in 2025. The county seat and the largest city is Ainsworth.

In the Nebraska license plate system, Brown County was represented by the prefix "75" (as it had the 75th-largest number of vehicles registered in the state when the license plate system was established in 1922).

Brown County was created on February 19, 1883 and named for two members of the legislature who reported the bill for the county's organization.

According to the United States Census Bureau, the county has a total area of 1,225.145 square miles (3,173.11 km²), of which 1,221.405 square miles (3,163.42 km²) is land and 3.740 square miles (9.69 km²) (0.31%) is water. It is the 10th-largest county in Nebraska by total area.

Brown County is located in Nebraska's Outback region.

As of the 2020 census, the county had a population of 2,903. The median age was 47.0 years. 20.5% of residents were under the age of 18 and 25.2% of residents were 65 years of age or older. For every 100 females there were 101.5 males, and for every 100 females age 18 and over there were 100.5 males age 18 and over.

The racial makeup of the county was 91.8% White, 0.1% Black or African American, 0.4% American Indian and Alaska Native, 0.3% Asian, 0.0% Native Hawaiian and Pacific Islander, 3.6% from some other race, and 3.9% from two or more races. Hispanic or Latino residents of any race comprised 6.1% of the population.

0.0% of residents lived in urban areas, while 100.0% lived in rural areas.