Marrowstone is a census-designated place (CDP) on Marrowstone Island in Jefferson County, Washington, United States. The population was 995 at the 2020 census. All Marrowstone addresses are in Nordland, Washington, and the ZIP code is 98358.

Marrowstone takes its name from Marrowstone Point, the northernmost point on Marrowstone Island. It was given the name "Marrow-Stone Point" in 1792 by the British explorer, George Vancouver, in describing the area's hard, clay-like soil.

A post office called Nordland has been in operation since 1898. The community derives its name from Peter Nordby, the original owner of the town site.

According to the United States Census Bureau, the CDP has a total area of 6.3 square miles (16.4 km), all of it land.

Prominent land features include several points, such as Marrowstone Point, at the northern end of Marrowstone Island, Kinney Point, at the southern end of the island, Nodule Point, on the east side, mid island, and Griffiths Point, on the western side of Mystery Bay, which is an inlet on the western side of Marrowstone Island. Other notable features include East Beach, a sandy beach at the northern end of East Marrowstone Road and Scow Bay/Kilisut Harbor, which separates Marrowstone Island from its western neighbor, Indian Island, a Navy ammunition depot.

A narrow causeway connects the southwestern end of Marrowstone Island with the southern end of Indian Island. A short bridge joins the western side of Indian Island to the mainland of Jefferson County.

Flagler Road (SR 116) runs along the western edge of Marrowstone Island, which is primarily low-lying. East Marrowstone Road runs along the eastern edge of the island, which consists largely of sandy bluffs, with the exception of the area near East Beach.

Historical population

Census	Pop.	Note	%±
2010	844		—
2020	995		17.9%
US Decennial Census 2020 Census

As of the census of 2010, there were 844 people, 432 households, and 260 families residing in the CDP. The population density was 133.5 people per square mile (51.5/km). There were 611 housing units at an average density of 96.6/sq mi (37.4/km). The racial makeup of the CDP was 96.4% White, 0.4% Native American, 0.8% Asian, 0.1% from other races, and 2.1% from two or more races. Hispanic or Latino of any race were 0.9% of the population.

There were 432 households, out of which 10.4% had children under the age of 18 living with them, 55.1% were married couples living together, 3.7% had a female householder with no husband present, and 39.8% were non-families. 30.3% of all households were made up of individuals, and 16.0% had someone living alone who was 65 years of age or older. The average household size was 1.95 and the average family size was 2.37.

In the CDP, the population skewed older with 90.5% 18 and over, 46.3% over 62, and 36.1% who were 65 years of age or older. The median age was 60.5 years. For every 100 males there were 98.1 females.

The median income for a household in the CDP was $48,533, and the median income for a family was $54,397. Males had a median income of $45,000 versus $26,607 for females. The per capita income for the CDP was $31,146. None of the families and 0.0% of the population were living below the poverty line.

The Nordland General Store is Marrowstone's only source of groceries. It is arguably the focal point of Marrowstone; on maps the town of Nordland (the address of all Marrowstone residents) is usually located at the site of the Nordland General Store. It is located across Flagler Road from Mystery Bay, near the center of Marrowstone Island. It was severely damaged by fire in November 2020, but reopened in May 2024.

For approximately 100 years, Marrowstone has held its annual Strawberry Festival in June. Residents and visitors enjoy strawberry shortcake at the Nordland Garden Club Building. The Marrowstone Island Community Association hosts the Strawberry Festival each year. It meets about 7 times throughout the year at the Nordland Garden Club Building. Strawberries were once grown all over Marrowstone and can be found growing wild on the island.

On Memorial Day weekend, island residents bring their tractors to parade them in front of the Nordland General Store.

The Seattle Youth Symphony's Marrowstone Music Festival - now called Marrowstone Summer Music and held on the campus of Western Washington University, in Bellingham, Washington – was held at Fort Flagler on the northern end of Marrowstone Island from 1958 until 1989. Until 1975, it was called the Pacific Northwest Music Camp.

The neo-pagan Aquarian Tabernacle Church performs a modern Eleusinian Mysteries play at Fort Flagler over Easter weekend each year.

Fort Flagler, a Washington state park, is situated on 784 acres (314 hectares) at the northern end of Marrowstone Island. It overlooks Port Townsend Bay and Admiralty Inlet, the entrance to Puget Sound. Fort Flagler was one of three forts, along with Fort Worden (near Port Townsend) and Fort Casey (on Whidbey Island), that guarded the entrance to Puget Sound. Mystery Bay State Park is another state park on Marrowstone Island, located on 10 acres (4 hectares) of Mystery Bay shorefront about a half-mile north of the Nordland General Store. It is primarily for boaters. Kinney Point State Park comprises 76 acres (310,000 m) at the south end of the island. Accessible only by boat, it is part of the Cascadia Marine Trail.

• Fort Flagler
• Marrowstone Island Information Portal