Lewiston is located at the confluence of the Snake and Clearwater Rivers. Its main industry is paper and timber products production at the mill owned and operated by the Clearwater Paper Corporation (until December 2008, a part of the Potlatch Corporation).
Because the portion of the Snake River between its confluence with the Columbia River near Pasco, Washington, and Lewiston is navigable by some ocean-going vessels, Lewiston has the distinction of being Idaho's only seaport and the western United States' farthest inland seaport. Barges of timber products, grain and other goods are shipped via the Snake-Columbia system to the Pacific Ocean. The Lower Granite Lock and Dam, the last of the four dams on the lower Snake River, was completed in 1972, raising the river level back to Lewiston.
As of the census of 2000, there were 30,905 people, 12,795 households, and 8,278 families residing in the city. The population density was 1,873.0 people per square mile (723.2/km²). There were 13,394 housing units at an average density of 811.8/sq mi (313.4/km²). The racial makeup of the city was 95.14% White, 0.30% African American, 1.59% Native American, 0.76% Asian, 0.08% Pacific Islander, 0.51% from other races, and 1.61% from two or more races. Hispanic or Latino of any race were 1.91% of the population.
There were 12,795 households out of which 28.7% included children under the age of 18, 51.3% were married couples living together, 9.3% had a female householder with no husband present, and 35.3% were non-families. 27.9% of all households were made up of individuals and 12.0% were a single person living alone who was 65 years of age or older. The average household size was 2.36 and the average family size was 2.88.
In the city the population was spread out with 23.3% under the age of 18, 10.7% from 18 to 24, 26.7% from 25 to 44, 22.3% from 45 to 64, and 17.0% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 95.3 males. For every 100 females age 18 and over, there were 92.1 males.
The median income for a household in the city was $36,606, and the median income for a family was $45,410. Males had a median income of $35,121 versus $22,805 for females. The per capita income for the city was $19,091. About 8.4% of families and 12.0% of the population were below the poverty line, including 15.2% of those under age 18 and 6.5% of those aged 65 or over.