Józef P. Dziekoński (1844-1927) is one of the most active creators in the field of sacred architecture at the turn of the 19th and 20th centuries, he is considered the architect of over a hundred churches. Based on source research, the author states that 66 churches were built according to Dziekoński's designs, 14 designs were not implemented, and over 10 were written incorrectly or have no archival confirmation. Among the churches built, the author distinguishes: early basilicas in the so-called transitional styles, basilica and hall churches in the Vistula-Baltic style and churches in the style of converted historicism (traditionalism). Another area of J. Dziekoński's activity was conservation work. According to his designs, four churches were restored, five were expanded and nine were rebuilt. In the period when the theoretical premises for the conservation of monuments were being developed, J. Dziekoński's design activity seemed representative of contemporary conservation projects, at least in the Kingdom of Poland.