Lawrence County was created on March 20, 1849, from parts of Beaver and Mercer counties. It was named after the USS Lawrence, Oliver Hazard Perry's original flagship at the Battle of Lake Erie during the War of 1812.
As of the census of 2000, there were 94,643 people, 37,091 households, and 25,889 families residing in the county. The population density was 263 people per square mile (101/km²). There were 39,635 housing units at an average density of 110 per square mile (42/km²). The racial makeup of the county was 94.98% White, 3.61% Black or African American, 0.10% Native American, 0.27% Asian, 0.01% Pacific Islander, 0.19% from other races, and 0.84% from two or more races. 0.56% of the population were Hispanic or Latino of any race. 26.1% were of Italian, 21.7% German, 9.3% Irish, 6.8% English and 6.8% Polish ancestry according to Census 2000.
There were 37,091 households out of which 28.80% had children under the age of 18 living with them, 54.50% were married couples living together, 11.50% had a female householder with no husband present, and 30.20% were non-families. 27.00% of all households were made up of individuals and 14.40% had someone living alone who was 65 years of age or older. The average household size was 2.47 and the average family size was 3.00.
In the county, the population was spread out with 23.10% under the age of 18, 8.30% from 18 to 24, 25.70% from 25 to 44, 23.60% from 45 to 64, and 19.30% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 90.60 males. For every 100 females age 18 and over, there were 86.90 males.