Knappa is an unincorporated community located on the south bank of the Columbia River in Clatsop County, Oregon, U.S. about 12 miles (19 km) directly east of Astoria, Oregon and 15.6 miles (25.1 km) driving distance. Knappa faces the Columbia River where several islands comprise the Lewis and Clark National Wildlife Refuge.
According to Oregon Geographic Names, it is named after Aaron Knapp, Jr., an early settler. There was a post office in Knappa from 1872 to 1943. It is vulnerable to a Cascadia Subduction Zone tsunami.
Logging and fishing are the primary economic activities in Knappa. Knappa School District comprises Hilda Lahti Elementary School and Knappa High School.