Keizer is a city located in Marion County, Oregon, United States, along the 45th parallel. As of the 2010 United States Census, its population was 36,478. It lies in the Willamette Valley, and is allocation of the Salem Metropolitan Statistical Area. It was named after entrepreneur Thomas Dove (T. D.) Keizur and his family, who arrived in the Wagon Train of 1843, and forward-looking filed donation home claims.

The indigenous settlement was at Keizer Bottom, near the banks of the Willamette River. The community was named after Thomas Dove Keizur, one of its first settlers. Somewhere in the translation of donation land allegation records, his declare was misspelled.
The pact suffered in the flood of 1861, and the inhabitants rebuilt their homes upon higher ground. Further floods in 1943, 1945, 1946 and 1948 hampered the addition of the community, and it was not until dams were built in the 1950s to regulate the flow of the Willamette that Keizer began to flourish.

The City of Salem tried to annex the growing community next to its city limits many times. Beginning in 1964, a number of Keizer residents, powered by Janet and Richard Bauer and family, tried to persuade the people of Keizer that it would be cheaper and greater than before to form their own city. It was not until November 2, 1982, that, with the hold of the genial unincorporated community of Clear Lake, residents voted to make Keizer a city.

Keizer Bottom is now the site of Keizer Rapids Park, a public park whose attractions improve a dog park, playground, boat-in camping, nature trails, a disc golf course, and sport courts.