According to the U.S. Census Bureau, the county has a total area of 4,015 km² (1,550 mi²). 3,631 km² (1,402 mi²) of it is land and 384 km² (148 mi²) of it is water. The total area is 9.57% water.
As of the census2 of 2000, there are 43,384 people, 17,585 households, and 11,834 families residing in the county. The population density is 12/km² (31/mi²). There are 26,260 housing units at an average density of 7/km² (19/mi²). The racial makeup of the county is 98.08% White, 0.23% Black or African American, 0.50% Native American, 0.27% Asian, 0.02% Pacific Islander, 0.21% from other races, and 0.69% from two or more races. 0.75% of the population are Hispanic or Latino of any race.
There are 17,585 households out of which 28.80% have children under the age of 18 living with them, 56.40% are married couples living together, 7.40% have a female householder with no husband present, and 32.70% are non-families. 28.30% of all households are made up of individuals and 13.30% have someone living alone who is 65 years of age or older. The average household size is 2.38 and the average family size is 2.92.
In the county, the population is spread out with 23.50% under the age of 18, 8.10% from 18 to 24, 25.90% from 25 to 44, 25.00% from 45 to 64, and 17.60% who are 65 years of age or older. The median age is 40 years. For every 100 females there are 97.50 males. For every 100 females age 18 and over, there are 95.00 males.