2006 38,241 2000 39,256 1990 39,884 1980 41,838 1970 41,546 1960 41,561 1950 43,415 1940 43,973 1930 43,813 1920 46,195 1910 39,183 1900 32,746 1890 28,044 1880 26,324 1870 21,562 1860 16,056 1850 11,084 1840 10,657 1830 6,525 1820 5,437 1810 7,945 1800 2,517
As of the census of 2000, there were 39,256 people, 15,552 households, and 10,139 families residing in the county. The population density was 76 people per square mile (29/km²). There were 17,305 housing units at an average density of 34 per square mile (13/km²). The racial makeup of the county was 96.37% White, 1.85% Black or African American, 0.21% Native American, 0.52% Asian, 0.05% Pacific Islander, 0.31% from other races, and 0.69% from two or more races. 0.82% of the population were Hispanic or Latino of any race. 28.5% were of American, 26.3% German, 10.1% English and 8.2% Irish ancestry according to Census 2000.
By 2005 the Latino population of Knox County had risen to 1.0%. African-Americans were 2.1% of the population.
In 2000 there were 15,552 households out of which 30.00% had children under the age of 18 living with them, 51.60% were married couples living together, 10.20% had a female householder with no husband present, and 34.80% were non-families. 29.70% of all households were made up of individuals and 13.30% had someone living alone who was 65 years of age or older. The average household size was 2.36 and the average family size was 2.93.
In the county the population was spread out with 22.90% under the age of 18, 13.60% from 18 to 24, 25.40% from 25 to 44, 22.70% from 45 to 64, and 15.40% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 98.50 males. For every 100 females age 18 and over, there were 95.60 males.
The median income for a household in the county was $31,362, and the median income for a family was $41,273. Males had a median income of $30,536 versus $20,916 for females. The per capita income for the county was $16,085. About 11.60% of families and 16.00% of the population were below the poverty line, including 19.70% of those under age 18 and 12.40% of those age 65 or over.
Knox County Indiana employers give high marks to their workforce when it comes to measuring productivity levels. The annual employee turnover rate is less than 5 percent, and absenteeism rates range from 0-3 percent per month.