This article elaborates the ways of popularising knowledge about the past of Mazovia by Museum in Płock since its establishment, as part of the Płock Scientific Society, in 1821. It had a strictly regional character. The collection consisted, on the one hand, of school teaching aids (minerals, physical and chemical equipment, globes, etc.), and on the other hand, of various exhibits donated by teachers, students, landowners, military personnel and priests, including numerous archaeological artefacts, coins, medals, natural history specimens, documents, etc. During scientific meetings, the latest archaeological and numismatic troves were reported, field inspections were organised, historical monuments were collected and placed in the museum. The institution was closed down shortly after the fall of the November Uprising. It was reactivated at the beginning of the 20th century. In December 1912, a permanent exhibition depicting the geological and historical past and the ethnography of Płock Mazovia was opened in the Gothic canonry at 8 Kanoniczny Square. In 1930, the premises were enlarged by the purchase of the House under Providence at 2 Kanoniczny Square, where the expositions of nature, geology, ethnography and archaeology were arranged. Until 1949, the facility, called the Mazovian Museum in Płock, was a part of the Płock Scientific Society. Afterwards, a new stage in its history began – a stage of independent development. The construction of a petrochemical plant in Płock in the 1960s contributed to the significant development of the facility. It obtained new premises in the renovated Castle of the Mazovian Dukes in Płock (Benedictine Abbey) on Tumskie Hill, which resulted in an increase in exhibition space and the number of specialised employees. In 1993, the Museum obtained the building of a historic granary on the Vistula embankment, where the collections of the Ethnography Department were located. In November 2004, the collections were moved from the Castle of the Mazovian Dukes to an art nouveau tenement house at 8 Tumska Street and a permanent Art Nouveau exhibition was arranged there. In the following years, the museum developed dynamically, in terms of its premises, its programme of activities, including the popularisation of historical knowledge. New museum pavilions and new permanent exhibitions were created. At present, the popularisation activity of the Mazovian Museum in Płock comprises a wide range of activities carried out by the Dissemination and Promotion Department and individual substantive departments. These include museum lessons, historical lectures, scientific sessions, workshops for children and people with disabilities, outdoor events, promotions of publications, concerts, competitions, educational films, periodicals (“Rocznik Muzeum Mazowieckiego w Płocku”, “Nasze Korzenie”, “Biuletyn Muzealny”), paratheatrical performances and many others. Key words: cultural heritage of Mazovia, regionalism, popularisation of historical knowledge, Mazovian Museum in Płock, Płock Scientific Society