The article reflects the study of the Russian part of Altai as the Siberian frontier, presented in the geographical lexicons of the Russian Empire of the 18th century, compiled by V. N. Tatishchev, F. A. Polunin and L. M. Maksimovich. Toponyms of this region not only contain cultural and historical information, but also reflect the processes of national and territorial identity through linguistic and cultural ideas. For the analysis, the historical method of onomastics was used using stratification and a detailed description of the material, as well as a lexicographic analysis of toponyms with linguocultural commentary. The reflection of toponyms characterizing the development of the territories of the south of Western Siberia in geographical lexicographical sources of the 18th century indicates changes in their perception in the context of “friend or foe” and the possible completion of the frontier stage (or transition to the post-frontier stage).