[3] It is named for David Williams, one of the captors of John André in the American Revolutionary War.

[5] As of the census[10] of 2000, there were 39,188 people, 15,105 households, and 10,664 families living in the county.

The racial makeup of the county was 96.51% White, 0.72% Black or African American, 0.23% Native American, 0.52% Asian, 0.01% Pacific Islander, 1.19% from other races, and 0.83% from two or more races.

43.6% were of German, 17.7% American, 8.1% English and 5.8% Irish ancestry according to Census 2000.

24.90% of all households were made up of individuals, and 10.50% had someone living alone who was 65 years of age or older.

As of the 2010 United States Census, there were 37,642 people, 15,075 households, and 10,260 families living in the county.

[11] In terms of ancestry, 46.1% were German, 12.0% were Irish, 10.7% were English, and 7.8% were American.

Current commissioners are: Brian Davis, Lewis Hilkert, and Terry Rummel.