In recent years, average temperatures in the county seat of Tuscola have ranged from a low of 18 °F (−8 °C) in January to a high of 88 °F (31 °C) in July, although a record low of −26 °F (−32 °C) was recorded in December 1989 and a record high of 113 °F (45 °C) was recorded in July 1954. Average monthly precipitation ranged from 2.12 inches (54 mm) in February to 4.64 inches (118 mm) in July.
As of the 2010 United States Census, there were 19,980 people, 7,720 households, and 5,377 families residing in the county. The population density was 48.0 inhabitants per square mile (18.5/km2). There were 8,390 housing units at an average density of 20.1 per square mile (7.8/km2). The racial makeup of the county was 95.7% white, 0.4% Asian, 0.3% black or African American, 0.2% American Indian, 2.3% from other races, and 1.2% from two or more races. Those of Hispanic or Latino origin made up 6.1% of the population. In terms of ancestry, 29.6% were German, 12.6% were American, 12.1% were English, and 10.7% were Irish.
Of the 7,720 households, 32.6% had children under the age of 18 living with them, 57.0% were married couples living together, 8.5% had a female householder with no husband present, 30.3% were non-families, and 26.1% of all households were made up of individuals. The average household size was 2.57 and the average family size was 3.11. The median age was 38.7 years.
The median income for a household in the county was $46,941 and the median income for a family was $60,352. Males had a median income of $41,318 versus $28,731 for females. The per capita income for the county was $21,438. About 7.1% of families and 10.2% of the population were below the poverty line, including 14.0% of those under age 18 and 7.2% of those age 65 or over.
Douglas is a powerfully Republican county. Apart from a narrow plurality of thirty-two votes to Bill Clinton in 1992, it has voted Republican in every Presidential election since 1968, and in all but five overall since 1880. Despite its long-time Republican leanings, Hillary Clinton’s 2016 performance of gaining a mere 23.8 percent of the county’s vote stands over six percent worse than any Democrat since the Civil War.