Marietta-Alderwood is a census-designated place (CDP) in Whatcom County, Washington, United States.

Parts of Marietta-Alderwood were annexed into Bellingham in 2019, while the rest remains an unincorporated area.

This region experiences warm (but not hot) and dry summers, with no average monthly temperatures above 71.6 °F.

There were 1,606 housing units at an average density of 268.8 per square mile (103.8/km2).

27.4% of all households were made up of individuals, and 6.8% had someone living alone who was 65 years of age or older.