Dauphin County was created on March 4, 1785, from part of Lancaster County and was named after Louis-Joseph, Dauphin of France the first son of Louis XVI. Louis-Joseph's title of Dauphin signified that he was the heir apparent to the throne of France. The county seat is Harrisburg.
As of the census of 2000, there were 251,798 people, 102,670 households, and 66,119 families residing in the county. The population density was 479 people per square mile (185/km²). There were 111,133 housing units at an average density of 212 per square mile (82/km²). The racial makeup of the county was 77.11% White, 16.91% Black or African American, 0.16% Native American, 1.96% Asian, 0.03% Pacific Islander, 1.97% from other races, and 1.85% from two or more races. 4.13% of the population were Hispanic or Latino of any race. 29.2% were of German, 7.5% Irish, 7.3% American and 7.2% Italian ancestry according to Census 2000. 91.8% spoke English and 3.9% Spanish as their first language.
According to 2005 estimates, 73.9% of the county's population was non-Hispanic whites. 17.8% of the population was African-Americans. 2.5% were Asians. Latinos now were 5.0% of the population.
In 2000 there were 102,670 households out of which 29.70% had children under the age of 18 living with them, 47.60% were married couples living together, 12.90% had a female householder with no husband present, and 35.60% were non-families. 30.00% of all households were made up of individuals and 10.30% had someone living alone who was 65 years of age or older. The average household size was 2.39 and the average family size was 2.98.
In the county, the population was spread out with 24.30% under the age of 18, 7.60% from 18 to 24, 30.10% from 25 to 44, 23.80% from 45 to 64, and 14.20% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 92.30 males. For every 100 females age 18 and over, there were 88.80 males.