According to the United States Census Bureau, the city has a total area of 71.0 km² (27.4 mi²). 69.6 km² (26.9 mi²) of it is land and 1.3 km² (0.5 mi²) of it is water. The total area is 1.90% water.
As of the census of 2000, there are 55,532 people, 23,185 households, and 14,444 families residing in the city. The population density is 797.4/km² (2,065.2/mi²). There are 24,217 housing units at an average density of 347.7/km² (900.6/mi²). The racial makeup of the city is 94.78% White, 0.28% African American, 3.39% Native American, 0.45% Asian, 0.03% Pacific Islander, 0.17% from other races, and 0.89% from two or more races. 0.75% of the population are Hispanic or Latino of any race.
There are 23,185 households out of which 30.2% have children under the age of 18 living with them, 50.1% are married couples living together, 9.3% have a female householder with no husband present, and 37.7% are non-families. 31.0% of all households are made up of individuals and 10.5% have someone living alone who is 65 years of age or older. The average household size is 2.32 and the average family size is 2.94.
In the city the population is spread out with 23.5% under the age of 18, 11.1% from 18 to 24, 29.1% from 25 to 44, 22.4% from 45 to 64, and 13.8% who are 65 years of age or older. The median age is 36 years. For every 100 females there are 93.9 males. For every 100 females age 18 and over, there are 91.8 males.
The median income for a household in the city is $39,422, and the median income for a family is $51,477. Males have a median income of $33,804 versus $22,647 for females. The per capita income for the city is $20,789. 8.4% of the population and 5.7% of families are below the poverty line. Out of the total people living in poverty, 9.5% are under the age of 18 and 7.4% are 65 or older.