Hat Rock State Park, State park in eastern Oregon, United States.

Hat Rock State Park is a state park in eastern Oregon built around a basalt rock formation that rises above the Columbia River near Lake Wallula. The park includes boat ramps, fishing spots, a picnic area, and a small spring-fed pond alongside the main rock.

Hat Rock is thought to be an exposed remnant of a 12-million-year-old basalt flow, left bare by Ice Age floods. On October 19, 1805, William Clark wrote of "a rock on the Lard... resembling a hat", the first landmark the Lewis and Clark Expedition passed after reaching the Columbia River. Oregon State Parks bought 175 acres from Charles and Eileen Kirk in 1951 for $5,000 during construction of McNary Dam, and leased 191 more acres from the Army Corps of Engineers in 1953.

The name comes from the rock's profile, which William Clark likened to a hat in his journal entry of October 19, 1805. Today the park is used for hiking, horseback riding, picnicking, fishing and boat launching on Lake Wallula.

The park is open year-round and works well for a short stop or a longer outing with a boat or fishing gear. Boat ramps, picnic areas, and restrooms are clearly marked and easy to find once inside the park.

Hat Rock is about 70 feet (21 m) tall and, with Boat Rock nearby, is thought to be an exposed remnant of a basalt flow roughly 12 million years old, left bare by Ice Age floods. It is one of the few landmarks from the Lewis and Clark route along the Columbia that the river has not submerged.