A district called Hameln was established in 1885 within the
Prussian
Province of Hanover. At that time the city of
Pyrmont was part of the Principality of
Waldeck-Pyrmont. In 1921 Pyrmont decided in a plebiscite to leave Waldeck-Pyrmont and to join Prussia. The Prussian administration assigned the city to the district of Hameln, which was renamed to Hameln-Pyrmont. In 1923
Hameln became a district-free city and was not part of the district until 1973, when it was reincorporated. Further enlargements of the district's territory took place in 1974 and 1977, when the cities of
Bad Münder and
Hessisch Oldendorf joined the district. ==Geography==