The 11th edition of the “Flora of the Central Part of European Russia” by P. F. Maevsky (2014) cites 1055 plant species for the Kostroma Region, but 83 species known from other contemporary sources were missed, of which 55 species are known from the materials collected and published before 2012. 28 species were found in the Kostroma Region in recent times, and four of them are missing from the “Flora…” – Cystopteris montana (Lam.) Desv., Carex bergrothii Palmgr., C. mackenziei V. Krecz., and Veronica urticifolia Jacq. On the contrary, 44 species are erroneously reported for the Kostroma Region. A list of additions and corrections with corresponding references to the literature and herbaria is presented. According to our data, the flora of the Kostroma Region includes at least 1130 species.