Mattawa is an incorporated city in Grant County, Washington, United States.

[4] The town of Mattawa was originally platted in 1909 by E. and Eva Campbell, but was not incorporated at that time.

[8] Mattawa is also home to the first straw bale library in the United States.

According to the United States Census Bureau, the town has a total area of 0.74 square miles (1.92 km2), all of it land.

There were 843 housing units at an average density of 1,139.2 per square mile (439.8/km2).

2.3% of all households were made up of individuals, and 0.6% had someone living alone who was 65 years of age or older.

5.5% of all households were made up of individuals, and 2.0% had someone living alone who was 65 years of age or older.