The Museum Association of Novo mesto began collecting museum pieces and archives for the future Dolenjska Museum Novo mesto in 1935. In 1945 the regional archive was established within the museum. Following the Law on Archival Material and Archives of 1966, all municipalities from the region of Dolenjska and Bela krajina gradually entrusted their collections to the Municipal Archives of Ljubljana (since 1973 the Historical Archives Ljubljana). In 1973 a special unit was established for these regions in Novo mesto, covering Dolenjska and Bela krajina; today it encompasses four sections: Črnomelj, Metlika, Novo mesto and Trebnje.
The majority of the records held here document 19th-century regional administration units, tribunals, banks, loan companies, associations and schools. There are only a few documents from the period of the Second World War. On the other hand, the archives provide excellent coverage of the period after 1945, with the exception of commerce documentation. Courts of justice, banks, loan companies, associations and schools are well documented.
The unit holds more than 520 records, representing some 1,800 linear metres of documents, the oldest dating from 1621. A reference library, a microfilm laboratory, and copying machines are available for use by members of the public.
There is enough room for exhibitions within the section of the unit in the Grm castle of Novo mesto. In 2008 there was an exhibition You will recognise them for their products, which dealt with the products of certain trades during the two world wars in Novo mesto.