Jantzen Beach Amusement Park was a popular amusement park from 1928 to 1970 in Portland, Oregon, on Hayden Island in the middle of the Columbia River. "The Coney Island of the West" opened on May 26, 1928 as the largest amusement park in the nation, covering over 123 acres (0.50 km2) at the northern tip of Portland.
In 1927, William A. Logus and Leo F. Smith purchased 40 acres (160,000 m2) of land on Hayden Island from the Portland Electric Power Company. Logus and Smith headed the Hayden Island Amusement Company and they built an amusement resort and tourist park named Jantzen Beach Amusement Park for one of the park's investors, Carl Jantzen, of Jantzen swimsuit fame. The door opened to the public on May 26, 1928. It surpassed all attendance expectations; over 30 million people patronized the park through its 42 years.
On opening day, Saturday May 26, 1928, 15,000 people paid the $0.10 admission. The following day, 25,000 people came out to the park. The amusement park included a merry-go-round, fun house, Big Dipper roller coaster, Golden Canopy Ballroom, four swimming pools, a natatorium, 25 acres (100,000 m2) of picnic grounds, and 15 acres (61,000 m2) of parking.
The C.W. Parker merry-go-round, built in 1921, was moved to Jantzen Beach in 1927. Some of the hand carved horses were made by inmates of the United States Penitentiary in Leavenworth, Kansas. The amusement park's popularity peaked during the 1940s.
In the late 1950s, attendance declined while, unrelatedly, the commercial value of the land increased. The park closed on Labor Day, 1970. The pumping system from the swimming pools remains and is used to pump drinking water to residents of Hayden Island. The C. W. Parker Four-Row Park Carousel (merry-go-round) was installed inside the Jantzen Beach Mall, a shopping mall located on the grounds formerly occupied by the park, and it operated there from 1972 to 2012. However, it was removed in 2012 for reconstruction of the shopping center, and it remains in storage in 2016. The carousel was added to the National Register of Historic Places in 1987 but removed in 2008.