As of the census of 2000, there were 218,590 people, 79,667 households, and 60,387 families residing in the county. The population density was 496 people per square mile (192/km²). There were 83,146 housing units at an average density of 189 per square mile (73/km²). The racial makeup of the county was 86.77% White, 9.27% Black or African American, 0.23% Native American, 1.52% Asian, 0.06% Pacific Islander, 0.69% from other races, and 1.47% from two or more races. 1.91% of the population were Hispanic or Latino of any race. 22.5% were of German, 13.1% Irish, 9.8% Italian, 9.2% English, 8.1% "American" and 6.0% Polish ancestry according to Census 2000.
By 2006 the population of Harford County had risen 10.4% to 241,402.
The 2005 report on race and ethnicity indicated the county's population was 82.8% non-Hispanic whites. The proportion of African-Americans in the county had risen to 11.5%. Hispanics were now 2.4% of the total population.
In 2000 there were 79,667 households out of which 38.70% had children under the age of 18 living with them, 61.90% were married couples living together, 10.20% had a female householder with no husband present, and 24.20% were non-families. 19.70% of all households were made up of individuals and 6.80% had someone living alone who was 65 years of age or older. The average household size was 2.72 and the average family size was 3.14.
In the county the population was spread out with 27.90% under the age of 18, 6.80% from 18 to 24, 31.60% from 25 to 44, 23.70% from 45 to 64, and 10.10% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 96.00 males. For every 100 females age 18 and over, there were 92.50 males.
The median income for a household in the county was $57,234, and the median income for a family was $63,868. Males had a median income of $43,612 versus $30,741 for females. The per capita income for the county was $24,232. About 3.60% of families and 4.90% of the population were below the poverty line, including 5.80% of those under age 18 and 6.70% of those age 65 or over.