According to the U.S. Census Bureau, the county has a total area of 1,030 square miles (2,700 km2), of which 999 square miles (2,590 km2) is land and 31 square miles (80 km2) (3.0%) is water. Native vegetation based on NRCS soils information shows:
In recent years, average temperatures in the county seat of Bagley have ranged from a low of −5 °F (−21 °C) in January to a high of 79 °F (26 °C) in July, although a record low of −53 °F (−47 °C) was recorded in February 1996 and a record high of 103 °F (39 °C) was recorded in August 1976. Average monthly precipitation ranged from 0.64 inches (16 mm) in December to 4.62 inches (117 mm) in June.
There were 3,330 households out of which 30.60% had children under the age of 18 living with them, 56.80% were married couples living together, 7.50% had a female householder with no husband present, and 31.30% were non-families. 27.90% of all households were made up of individuals and 14.50% had someone living alone who was 65 years of age or older. The average household size was 2.48 and the average family size was 3.02.
In the county the population was spread out with 26.00% under the age of 18, 7.60% from 18 to 24, 24.60% from 25 to 44, 24.30% from 45 to 64, and 17.50% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 101.10 males. For every 100 females age 18 and over, there were 100.30 males.
The median income for a household in the county was $30,517, and the median income for a family was $39,698. Males had a median income of $29,338 versus $20,417 for females. The per capita income for the county was $15,694. About 11.00% of families and 15.10% of the population were below the poverty line, including 18.90% of those under age 18 and 18.20% of those age 65 or over.