It was founded originally in 1840 as Anomickee County. In 1843, the name was changed to Alpena, a pseudo-Native American word — a neologism coined by Henry Schoolcraft, meaning something like "a good partridge country." This was part of a much larger effort to rename a great many of the Michigan counties at the time.
Alpena County was officially organized in 1857.
As of the 2000 census, there were 31,314 people, 12,818 households, and 8,690 families residing in the county. The population density was 54 inhabitants per square mile (20.8/km²). There were 15,289 housing units at an average density of 27/sq mi (10.4/km²). The racial makeup of the county was 98.21% White, 0.25% Black or African American, 0.39% Native American, 0.33% Asian, 0.12% from other races, and 0.70% from two or more races. 0.58% of the population were Hispanic or Latino of any race. 24.9% were of German, 23.2% Polish, 9.6% French, 6.9% English, 6.5% American and 5.8% Irish ancestry according to Census 2000. 96.7% spoke English and 1.1% German as their first language.
There were 12,818 households out of which 29.40% had children under the age of 18 living with them, 55.30% were married couples living together, 9.00% had a female householder with no husband present, and 32.20% were non-families. 27.80% of all households were made up of individuals and 13.30% had someone living alone who was 65 years of age or older. The average household size was 2.40 and the average family size was 2.93.
In the county the population was spread out with 23.70% under the age of 18, 7.80% from 18 to 24, 26.50% from 25 to 44, 24.90% from 45 to 64, and 17.10% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 94.60 males. For every 100 females age 18 and over, there were 92.50 males.
The median income for a household in the county was $34,177, and the median income for a family was $42,366. Males had a median income of $34,571 versus $21,962 for females. The per capita income for the county was $17,566. About 7.70% of families and 10.50% of the population were below the poverty line, including 13.10% of those under age 18 and 6.80% of those age 65 or over.