Ottawa County is part of the Toledo Metropolitan Statistical Area.
As of the census of 2000, there were 40,985 people, 16,474 households, and 11,729 families residing in the county. The population density was 161 people per square mile (62/km²). There were 25,532 housing units at an average density of 100 per square mile (39/km²). The racial makeup of the county was 96.56% White, 0.65% Black or African American, 0.21% Native American, 0.23% Asian, 0.05% Pacific Islander, 1.44% from other races, and 0.87% from two or more races. 3.75% of the population were Hispanic or Latino of any race.
There were 16,474 households out of which 29.10% had children under the age of 18 living with them, 58.90% were married couples living together, 8.50% had a female householder with no husband present, and 28.80% were non-families. 25.00% of all households were made up of individuals and 11.20% had someone living alone who was 65 years of age or older. The average household size was 2.45 and the average family size was 2.92.
In the county, the population was spread out with 23.30% under the age of 18, 6.70% from 18 to 24, 26.80% from 25 to 44, 26.80% from 45 to 64, and 16.40% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 97.50 males. For every 100 females age 18 and over, there were 94.70 males.
The median income for a household in the county was $44,224, and the median income for a family was $51,919. Males had a median income of $39,823 versus $24,727 for females. The per capita income for the county was $21,973. About 4.20% of families and 5.90% of the population were below the poverty line, including 7.40% of those under age 18 and 5.40% of those age 65 or over.