The history of the Russian Cossacks of Transbaikalia and their role in the Russian borders control were highlighted in the first decades of the XXth century. The works by A. R. Artemyev, A. S. Zuyev, N. N. Smirnov, V. P. Trut, and Yu. L. Kasyanov should be mentioned among publications on this subject. In particular Dmitriyev A. V. studied the border control by the regular army’s units. The author, considering the research results of the mentioned above scientists, on the basis of archival data examines the difficulties in the activity of the Transbaikalia Cossacks and the regular army’s units, concerned geographical research and mapping of border areas.