According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. It is intersected by the Cedar and Wapsipinicon rivers.
The 2010 census recorded a population of 24,276 in the county, with a population density of. There were 9,915 housing units, of which 9,385 were occupied.
2000 census
As of the census of 2000, there were 23,325 people, 8,860 households, and 6,326 families residing in the county. The population density was 53 people per square mile. There were 9,337 housing units at an average density of 21 per square mile. The racial makeup of the county was 98.22% White, 0.48% Black or African American, 0.06% Native American, 0.52% Asian, 0.02% Pacific Islander, 0.10% from other races, and 0.60% from two or more races. 0.56% of the population were Hispanic or Latino of any race. There were 8,860 households out of which 32.00% had children under the age of 18 living with them, 62.50% were married couplesliving together, 6.20% had a female householder with no husband present, and 28.60% were non-families. 24.70% of all households were made up of individuals and 12.70% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 2.95. In the county, the population was spread out with 24.10% under the age of 18, 12.00% from 18 to 24, 23.90% from 25 to 44, 23.90% from 45 to 64, and 16.00% who were 65 years of age or older. The median age was 38 years. For every 100 females, there were 93.60 males. For every 100 females age 18 and over, there were 89.30 males. The median income for a household in the county was $40,826, and the median income for a family was $50,299. Males had a median income of $34,212 versus $22,250 for females. The per capita income for the county was $19,199. About 2.90% of families and 5.10% of the population were below the poverty line, including 4.20% of those under age 18 and 5.80% of those age 65 or over.
The is held at the county fairgrounds in Waverly every year in early August. It celebrated its 135th year in August 2010. Attractions include livestock and craft exhibitions, truck and tractor pulls, commercial and local exhibits, and various contests, performances, and concerts. The Bremer County Court House, which opened in 1937, is listed on the National Register of Historic Places. The was originally built in 1862 as a stagecoach stop and hotel. It is listed on the National Register of Historic Places.
