Franklin County is part of the Springfield Metropolitan Statistical Area.
As of the census of 2000, there were 71,535 people, 29,466 households, and 18,416 families residing in the county. The population density was 102 people per square mile (39/km²). There were 31,939 housing units at an average density of 46 per square mile (18/km²). The racial makeup of the county was 95.40% White, 0.89% Black or African American, 0.29% Native American, 1.04% Asian, 0.03% Pacific Islander, 0.75% from other races, and 1.61% from two or more races. 1.99% of the population were Hispanic or Latino of any race. 16.2% were of English, 12.2% Irish, 12.0% Polish, 10.2% French, 7.0% French Canadian, 6.7% German, 6.1% Italian and 6.0% American ancestry according to Census 2000. 94.5% spoke English and 1.8% Spanish as their first language. Historically a largely agrarian, rural county (much of it remains this way today), the area's sizable Irish contingent adopted the work ethic and subtle sense of entitlement displayed by the old Yankee families which first settled here after tribes like the Pocumtuc were pushed out or killed. Evidence of this allegiance can be seen in the plethora of Roman Catholic churches built to resemble Congregational 'meeting houses', and can be heard when speaking to descendants of Irish settlers, many of whom attribute farming, not factory labor, as their family's historical profession.
There were 29,466 households out of which 29.5% had children under the age of 18 living with them, 47.9% were married couples living together, 10.6% had a female householder with no husband present, and 37.5% were non-families. 29.0% of all households were made up of individuals and 10.9% had someone living alone who was 65 years of age or older. The average household size was 2.38 and the average family size was 2.95.
In the county the population was spread out with 23.5% under the age of 18, 7.8% from 18 to 24, 28.5% from 25 to 44, 25.9% from 45 to 64, and 14.2% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 93.8 males. For every 100 females age 18 and over, there were 90.5 males.