As of the census of 2000, there are 8,154 people, 3,458 households, and 2,147 families residing in the city of Iron Mountain. The population density is 437.3/km˛ (1,132.6/mi˛). There are 3,819 housing units at an average density of 204.8/km˛ (530.5/mi˛). The racial makeup of the city of Iron Mountain is 97.67% White, 0.20% African American, 0.48% Native American, 0.66% Asian, 0.01% Pacific Islander, 0.23% from other races, and 0.75% from two or more races. 1.07% of the population are Hispanic or Latino of any race.

There are 3,458 households out of which 30.0% have children under the age of 18 living with them, 48.8% are married couples living together, 9.6% have a female householder with no husband present, and 37.9% are non-families. 33.3% of all households are made up of individuals and 16.2% have someone living alone who is 65 years of age or older. The average household size is 2.29 and the average family size is 2.94.

In the city of Iron Mountain the population is spread out with 25.1% under the age of 18, 7.1% from 18 to 24, 27.2% from 25 to 44, 21.1% from 45 to 64, and 19.6% who are 65 years of age or older. The median age is 39 years. For every 100 females there are 96.4 males. For every 100 females age 18 and over, there are 90.6 males.

The median income for a household in the city of Iron Mountain is $32,526, and the median income for a family is $43,687. Males have a median income of $38,309 versus $22,533 for females. The per capita income for the city is $19,918. 10.6% of the population and 9.4% of families are below the poverty line. Out of the total people living in poverty, 13.5% are under the age of 18 and 10.5% are 65 or older.