Smith County is part of the Tyler Metropolitan Statistical Area as well as the Tyler–Jacksonville Combined Statistical Area.
As of the census of 2000, there were 174,706 people, 65,692 households, and 46,904 families residing in the county. The population density was 188 people per square mile (73/km²). There were 71,701 housing units at an average density of 77 per square mile (30/km²). The racial makeup of the county was 71.61% White, 20.06% Black or African American, 0.43% Native American, 0.70% Asian, 0.03% Pacific Islander, 5.74% from other races, and 1.44% from two or more races. 11.17% of the population were Hispanic or Latino of any race.
There were 65,692 households out of which 33.10% had children under the age of 18 living with them, 55.50% were married couples living together, 12.30% had a female householder with no husband present, and 28.60% were non-families. 24.70% of all households were made up of individuals and 9.80% had someone living alone who was 65 years of age or older. The average household size was 2.59 and the average family size was 3.10.
In the county, the population was spread out with 26.60% under the age of 18, 9.80% from 18 to 24, 27.40% from 25 to 44, 22.10% from 45 to 64, and 14.10% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 92.10 males. For every 100 females age 18 and over, there were 87.90 males.
The median income for a household in the county was $37,148, and the median income for a family was $44,534. Males had a median income of $32,451 versus $22,351 for females. The per capita income for the county was $19,072. About 10.20% of families and 13.80% of the population were below the poverty line, including 18.40% of those under age 18 and 10.80% of those age 65 or over.