The James River flows south-southeastward through the eastern central part of Beadle County. The terrain of Beadle County consists of low rolling hills, sloping toward the river valley. The county's highest point is its SW corner, at 1,841' ASL. Its lowest point is on the southboundary line, where James River flows into adjacent Sanborn County, at 1,230' ASL. The county has a total area of, of which is land and is water.
As of the 2000 United States Census, there were 17,023 people, 7,210 households, and 4,535 families in the county. The population density was 14 people per square mile. There were 8,206 housing units at an average density of 6 per square mile. The racial makeup of the county was 96.93% White, 0.69% Black or African American, 0.95% Native American, 0.31% Asian, 0.02% Pacific Islander, 0.26% from other races, and 0.85% from two or more races. 0.91% of the population were Hispanic or Latino of any race. 49.9% were of German, 11.7% Norwegian, 6.1% Irish, 5.8% English and 5.5% United States or American ancestry. There were 7,210 households out of which 28.30% had children under the age of 18 living with them, 52.50% were married couplesliving together, 7.40% had a female householder with no husband present, and 37.10% were non-families. 33.10% of all households were made up of individuals and 15.00% had someone living alone who was 65 years of age or older. The average household size was 2.30 and the average family size was 2.94. The county population contained 24.70% under the age of 18, 8.30% from 18 to 24, 24.70% from 25 to 44, 23.00% from 45 to 64, and 19.40% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 96.60 males. For every 100 females age 18 and over, there were 93.70 males. The median income for a household in the county was $30,510, and the median income for a family was $40,596. Males had a median income of $26,910 versus $19,785 for females. The per capita income for the county was $17,832. About 7.90% of families and 11.90% of the population were below the poverty line, including 14.20% of those under age 18 and 12.30% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 17,398 people, 7,276 households, and 4,509 families residing in the county. The population density was. There were 8,304 housing units at an average density of. The racial makeup of the county was 89.7% white, 3.6% Asian, 1.1% American Indian, 0.8% black or African American, 0.1% Pacific islander, 3.0% from other races, and 1.6% from two or more races. Those of Hispanic or Latino origin made up 7.7% of the population. In terms of ancestry, 45.4% were German, 11.7% were Norwegian, 10.3% were Irish, 8.8% were English, and 4.1% were American. Of the 7,276 households, 28.6% had children under the age of 18 living with them, 49.5% were married couples living together, 8.3% had a female householder with no husband present, 38.0% were non-families, and 33.0% of all households were made up of individuals. The average household size was 2.31 and the average family size was 2.92. The median age was 41.2 years. The median income for a household in the county was $40,716 and the median income for a family was $56,288. Males had a median income of $37,020 versus $25,824 for females. The per capita income for the county was $23,409. About 6.3% of families and 13.1% of the population were below the poverty line, including 12.8% of those under age 18 and 12.5% of those age 65 or over.
Beadle County has become more Republican in recent history. In 2000, George W. Bush won the county, ending a streak of Democratic-majority voting that began in 1990.
