The county is the second-largest in the state in terms of area (trailing only Baldwin County) and sixth-largest in terms of population (behind Jefferson, Mobile, Madison, Montgomery,and Shelby counties).
Its seat and largest city is Tuscaloosa, the former state capital from 1826 to 1845. It is also the largest county in the Tuscaloosa, Alabama, Metropolitan Statistical Area.
As of the census of 2000, there were 164,875 people, 64,517 households, and 41,677 families residing in the county. The population density was 48 persons/km² (124/sq mi). The population core of the county lies in Tuscaloosa-Northport conurbation (including Coaling, Coker, and Holt CDP). The combined 2000 Census population of this area (not including their undesignated suburban census areas) is 103,367, accounting for 62.7% of the county in population, while only accounting for 6.9% in area. Consequently, the population density of the central population core is 439 persons/km² (1137 persons/sq mi), while the density of the county outside the central population core is only 17 persons/km² (44 persons/sq mi).
There were 71,429 housing units at an average density of 54/sq mi (21/km²). The racial makeup of the county was 68.12% White, 29.31% Black or African American, 0.23% Native American, 0.92% Asian, 0.03% Pacific Islander, 0.56% from other races, and 0.82% from two or more races. Nearly 1.29% of the population were Hispanic or Latino of any race.
There were 64,517 households, out of which 30.30% had children under the age of 18 living with them; 47.20% were married couples living together, 14.00% had a female householder with no husband present, and 35.40% were non-families. 28.40% of all households were made up of individuals, and 8.30% had someone living alone who was 65 years of age or older. The average household size was 2.42, and the average family size was 3.00.
In the county, the population was spread out with 23.40% under the age of 18, 16.50% from 18 to 24, 28.10% from 25 to 44, 20.80% from 45 to 64, and 11.30% who were 65 years of age or older. The median age was 32 years. For every 100 females, there were 92.80 males. For every 100 females age 18 and over, there were 89.50 males.
The median income for a household in the county was $34,436, and the median income for a family was $45,485. Males had a median income of $34,807 versus $24,128 for females. The per capita income for the county was $18,998. About 11.30% of families and 17.00% of the population were below the poverty line, including 19.50% of those under age 18 and 13.20% of those age 65 or over.