Lebanon County is part of the Lebanon Metropolitan Statistical Area and the Harrisburg–Carlisle–Lebanon Combined Statistical Area.
As of the census of 2000, there were 120,327 people and 32,771 families residing in the county. The population density was 332 people per square mile (128/km²). There were 49,320 housing units at an average density of 136 per square mile (53/km²). The racial makeup of the county was 94.46% White, 1.29% Black or African American, 0.13% Native American, 0.89% Asian, 0.04% Pacific Islander, 2.26% from other races, and 0.94% from two or more races. 4.96% of the population were Hispanic or Latino of any race. 45.6% were of German, 11.8% American and 6.1% Irish ancestry according to Census 2000. 92.5% spoke English, 4.2% Spanish and 1.1% Pennsylvania Dutch as their first language.
There were 46,551 households out of which 30.40% had children under the age of 18 living with them, 57.40% were married couples living together, 9.20% had a female householder with no husband present, and 29.60% were non-families. 25.20% of all households were made up of individuals and 11.10% had someone living alone who was 65 years of age or older. The average household size was 2.49 and the average family size was 2.98.
In the county, the population was spread out with 23.70% under the age of 18, 8.20% from 18 to 24, 28.00% from 25 to 44, 23.70% from 45 to 64, and 16.40% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 95.00 males. For every 100 females age 18 and over, there were 91.70 males.