Castle Rock is named for a volcanic rock outcropping over the Cowlitz River, "The Rock", rising 190 feet high on the south side of the city. The rock formation, resembling a castle, became a geographic landmark for Cowlitz Indians and Hudson's Bay Company traders as early as 1832. Today, it is the location of The Rock Community Park, with hiking trails, picnic tables, and a historical marker.
Castle Rock is centered primarily on the donation land claim of Eliza and William Huntington, who settled at the location in 1852. The city was platted December 12, 1888 and incorporated on June 20, 1890. Castle Rock prospered as a Cowlitz River steamboat port and trading center for valley farms. The local sawmill was the first to produce cedar shingles, using the Western red cedar, which grows in abundance in the region.
By 1940, the population had reached 1,182 and was supported by dairy farming, truck farming, and lumber manufacturing. Sword ferns, common in the region, were picked each year by several hundred people to be processed into medicine. In the spring, large quantities of Cascara Sagrada bark were gathered, dried, and shipped.
Castle Rock, the Gateway to Mount St. Helens, is 117 miles south of Seattle, Washington and 58 miles north of Portland, Oregon, 46°16′26″N 122°54′18″W (46.273991, −122.904916). Castle Rock is situated between the Cowlitz River and Interstate 5, one mile south of the confluence of the Cowlitz and the Toutle River. According to the United States Census Bureau, the city has a total area of 1.76 square miles (4.56 km2), of which, 1.59 square miles (4.12 km2) is land and 0.17 square miles (0.44 km2) is water. It is the northernmost city in Cowlitz County.
Spirit Lake Memorial Highway (State Route 504) connects the city to the Mount St. Helens National Volcanic Monument, the Spirit Lake recreation area, Seaquest State Park and Silver Lake. The State Route 504 Spur extends to Gifford Pinchot National Forest.
West Side Highway, running north along the Cowlitz River, connects Castle Rock to Cloud Mountain and the communities of Olequa and Vader, Washington. Continuing south, West Side Highway / State Route 411 connects Castle Rock to Longview, Washington, and Ocean Beach Highway (State Route 4), putting Castle Rock 75 miles from Willapa National Wildlife Refuge and the Pacific Ocean.
The Castle Rock Park & Ride is located on Huntington Avenue next to Interstate 5 Exit 49. Bus service is provided by Lower Columbia CAP Rural Public Transit to Longview and Chehalis, via Interstate 5.
The Riverfront Trail, a multi-use off-road trail, runs along both sides of the Cowlitz River. On the east side, the trail begins at Lions Pride Park, runs past the Rock Community Park, and 1.5 miles later reaches the PH10 bridge. On the west side, the trail runs 1100 feet to the Castle Rock Sports Complex. The City of Castle Rock was awarded the Association of Washington Cities 2004 Municipal Achievement Gold Medal Award for the city's trail system.
As of the census of 2010, there were 1,982 people, 784 households, and 519 families residing in the city. The population density was 1,246.5 inhabitants per square mile (481.3/km2). There were 863 housing units at an average density of 542.8 per square mile (209.6/km2). The racial makeup of the city was 91.4% White, 0.1% African American, 2.2% Native American, 0.2% Asian, 0.4% Pacific Islander, 1.7% from other races, and 4.0% from two or more races. Hispanic or Latino of any race were 4.9% of the population.
There were 784 households of which 32.7% had children under the age of 18 living with them, 43.5% were married couples living together, 16.3% had a female householder with no husband present, 6.4% had a male householder with no wife present, and 33.8% were non-families. 27.7% of all households were made up of individuals and 10.9% had someone living alone who was 65 years of age or older. The average household size was 2.53 and the average family size was 3.06.
The median age in the city was 39.3 years. 24.4% of residents were under the age of 18; 8.1% were between the ages of 18 and 24; 24.7% were from 25 to 44; 27% were from 45 to 64; and 15.9% were 65 years of age or older. The gender makeup of the city was 47.5% male and 52.5% female.
As of the census of 2000, there were 2,130 people, 833 households, and 562 families residing in the city. The population density was 1,597.3 people per square mile (618.3/km2). There were 890 housing units at an average density of 667.4 per square mile (258.4/km2). The racial makeup of the city was 93.19% White, 0.23% African American, 2.02% Native American, 0.28% Asian, 0.38% Pacific Islander, 1.64% from other races, and 2.25% from two or more races. Hispanic or Latino of any race were 3.33% of the population. 18.7% were of American, 18.3% German, 12.9% English, 6.9% Irish and 6.1% Norwegian ancestry. 96.5% spoke English, and 3.0% Spanish as their first language.
There were 833 households out of which 33.9% had children under the age of 18 living with them, 46.3% were married couples living together, 16.6% had a female householder with no husband present, and 32.5% were non-families. 28.2% of all households were made up of individuals and 13.4% had someone living alone who was 65 years of age or older. The average household size was 2.53 and the average family size was 3.07.
In the city, the age distribution of the population shows 29.4% under the age of 18, 7.5% from 18 to 24, 26.9% from 25 to 44, 22.7% from 45 to 64, and 13.6% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 86.0 males. For every 100 females age 18 and over, there were 83.5 males.
The median income for a household in the city was $37,212, and the median income for a family was $44,125. Males had a median income of $38,289 versus $25,000 for females. The per capita income for the city was $15,661. About 10.7% of families and 17.3% of the population were below the poverty line, including 20.9% of those under age 18 and 7.5% of those age 65 or over.
There are three schools in Castle Rock: Castle Rock Elementary, Castle Rock Middle School, and Castle Rock High School. The middle school's mascot is the Pirate, while The mascot for both the elementary school and the high school is the Rocket. In front of the high school is a rocket, the original rocket was built to be a military drone. There has since been a new rocket put up painted in the school colors of red and white.