In recent years, average temperatures in the county seat of Morris have ranged from a low of 13 °F (−11 °C) in January to a high of 85 °F (29 °C) in July, although a record low of −24 °F (−31 °C) was recorded in January 1985 and a record high of 103 °F (39 °C) was recorded in June 1988. Average monthly precipitation ranged from 1.59 inches (40 mm) in February to 4.16 inches (106 mm) in June.
There were 14,293 households out of which 35.30% had children under the age of 18 living with them, 59.60% were married couples living together, 8.60% had a female householder with no husband present, and 28.10% were non-families. 23.50% of all households were made up of individuals and 9.40% had someone living alone who was 65 years of age or older. The average household size was 2.60 and the average family size was 3.09.
In the county the population was spread out with 26.60% under the age of 18, 8.30% from 18 to 24, 30.20% from 25 to 44, 22.50% from 45 to 64, and 12.30% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 98.90 males. For every 100 females age 18 and over, there were 97.40 males.
The median income for a home in the county is $51,719, and the median income for a family was $60,862. Males had a median income of $46,392 versus $26,487 for females. The per capita income for the county was $22,591. About 3.20% of families and 4.80% of the population were below the poverty line, including 5.00% of those under age 18 and 6.00% of those age 65 or over.