2000 45,922 1990 42,836 1980 42,472 1970 38,038 1960 36,564 1950 34,346 1940 35,045 1930 35,583 1920 28,228 1910 30,625 1900 25,729 1890 19,792 1880 18,543 1870 14,628 1860 13,692 1850 12,097 1840 11,782 1830 9,234 1820 4,116
As of the census of 2000, there were 45,922 people, 18,535 households, and 13,141 families residing in the county. The population density was 102 people per square mile (40/km²). There were 20,560 housing units at an average density of 46 per square mile (18/km²). The racial makeup of the county was 97.92% White, 0.39% Black or African American, 0.28% Native American, 0.28% Asian, 0.01% Pacific Islander, 0.34% from other races, and 0.78% from two or more races. 0.91% of the population were Hispanic or Latino of any race. 32.9% were of American, 15.3% German, 14.3% English and 10.9% Irish ancestry according to Census 2000.
There were 18,535 households out of which 31.40% had children under the age of 18 living with them, 58.50% were married couples living together, 9.00% had a female householder with no husband present, and 29.10% were non-families. 25.50% of all households were made up of individuals and 11.50% had someone living alone who was 65 years of age or older. The average household size was 2.44 and the average family size was 2.91.
In the county the population was spread out with 24.60% under the age of 18, 7.70% from 18 to 24, 28.10% from 25 to 44, 25.00% from 45 to 64, and 14.80% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 95.10 males. For every 100 females age 18 and over, there were 91.50 males.
The median income for a household in the county was $36,280, and the median income for a family was $43,109. Males had a median income of $34,167 versus $21,647 for females. The per capita income for the county was $17,653. About 7.30% of families and 9.80% of the population were below the poverty line, including 11.60% of those under age 18 and 8.50% of those age 65 or over.
Lawrence County is the hometown of several astronauts. Virgil I. "Gus" Grissom was born and raised in Mitchell. Charles "Charlie" Walker was born and raised in Oolitic. Although he was born in Virginia, Kenneth "Kenny" Bowersox considers Bedford to be his hometown since that is where he was raised.