In 1945, he took a year's leave of absence from the FBI when he and Marie came back to Garden City, Kansas. Due to his father's illness, he was temporarily helping his mother in the operation of the Blue Bird Cabin Camp. That year, he was approached by the Democratic Party to run for office of Sherriff for Finney County. He won the election, resigned from the bureau, and served in that office for nine years until becoming a Special Agent of the KBI in 1955. While Sherriff, Dewey enlisted in the Kansas National Guard.
Over the next three years, Marie gave birth to both of their sons, Al the 3rd and Paul.
As the result of the successful investigation of the Clutter murder case, Dewey was requested by the U.S. Senate Committee on the Judiciary to appear before the Subcommittee on Constitutional Amendments in Washington, D.C. to discuss his opinion of the Supreme Court's decision in the case, Miranda v. Arizona. He disagreed with the decision of the case and outlined how adversely that decision would have affected the solving of the Clutter case.
In his memory, Marie established the Alvin A. Dewey Memorial Scholarship Fund at Garden City Community College in the Criminal Justice Department.