2020 census
As of the 2020 United States census, there were 45,463 people, 17,613 households, and 11,924 families residing in the parish.
2000 census
As of the census of 2000, there were 43,926 people, 16,467 households, and 11,642 families residing in the parish. The population density was 66 people per square mile (25/km2). There were 19,106 housing units at an average density of 28 per square mile (11/km2). The racial makeup of the parish was 67.42% White, 31.53% Black or African American, 0.23% Native American, 0.17% Asian, 0.11% from other races, and 0.54% from two or more races. 0.76% of the population were Hispanic or Latino of any race.
There were 16,467 households, out of which 32.70% had children under the age of 18 living with them, 49.30% were married couples living together, 17.10% had a female householder with no husband present, and 29.30% were non-families. 26.60% of all households were made up of individuals, and 12.50% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.09.
In the parish the population was spread out, with 26.80% under the age of 18, 9.50% from 18 to 24, 26.70% from 25 to 44, 22.60% from 45 to 64, and 14.30% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 95.40 males. For every 100 females age 18 and over, there were 92.80 males.
The median income for a household in the parish was $24,264, and the median income for a family was $29,480. Males had a median income of $27,964 versus $17,709 for females. The per capita income for the parish was $12,915. About 19.40% of families and 24.70% of the population were below the poverty line, including 32.20% of those under age 18 and 20.40% of those age 65 or over. Washington Parish has the second highest level of poverty in the state after Orleans Parish.
Economy
Washington Parish is currently known for its agriculture, particularly watermelons. Through much of the 20th century, its economy was based on its timber and paper industry.
In 1906, The Great Southern Lumber Company, founded by the Goodyear brothers from New York, purchased huge tracts of forest and established a sawmill in Bogalusa to harvest the local virgin pine forests. This company was the first to introduce reforestation in order to sustain the timber industry locally. Taken over by Crown Zellerbach, it later started a paper mill and chemical businesses in the area.
The local business passed through several hands as the lumber and related industries restructured through the late 20th century. In the 21st century, Temple-Inland Corporation is the largest employer in the parish.
Education
Students residing outside of Ward 4 attend Washington Parish School System. Students within Ward 4 attend Bogalusa City Schools.
Northshore Technical Community College is located in Bogalusa.
Corrections
Louisiana Department of Public Safety and Corrections operates the B.B. "Sixty" Rayburn Correctional Center in an unincorporated section of Washington Parish.
National Guard
Bogalusa is home to the headquarters of the 205th Engineer Battalion of the 225th Engineer Brigade. Franklinton is the home of the 843rd Engineer Company.
Communities
thumb|200px|Map of Washington Parish, Louisiana With Municipal Labels
City
Bogalusa (largest municipality)
Town
Franklinton (parish seat)
Villages
Angie
Varnado
Unincorporated communities
Enon
Mount Hermon
Pine
Thomas
Warnerton
Notable people
Oneal Moore (1931-1965), US Army veteran and first African-American deputy sheriff in Washington Parish Sheriff's Office; murdered while in uniform in a drive-by shooting, June 2, 1965. Case never solved.
Henry "Tank" Powell (born 1945), state representative from Tangipahoa Parish from 1996 to 2008; member of the Louisiana Board of Pardons since 2008
Weldon Russell (born 1946), former state representative for Tangipahoa and St. Helena parishes; born in Washington Parish
Malinda Brumfield White (born 1967), state representative for Washington and St. Tammany parishes, effective 2016
Katherine Haik (born 2000), from Franklinton, named Miss Teen USA 2015 at the age of fifteen