The purpose of the article is to analyze the activities of Johann Cornies who was an informal leader of the Mennonite colonies at the first half of the 19th century. Research methods. The author uses general historical research methods, analysis of sources and contemporary historiography to recreate the image of this article hero. Results. A skillful owner and a successful entrepreneur, Cornies ran a number of business associations (“Forestry Society”, “Society for the Improvement of Agriculture, Industry and Commerce Union”) founded by the Mennonites at the request of the Guardianship Committee. In 1820–1848 Cornies focused his activities on a comprehensive and interrelated process of the settlements’ and the region’s development. Those included the tasks of economic development and the search for this region specialization, as well as market relations introduction, administrative integration, colonization, social assimilation and ethnic consolidation. Cornies was motivated by his conviction of the importance of the market way of the Mennonite and surrounding settlements’ development. His innovative projects impacted the economic promotion of the settlements (their ways of agriculture, fine-fleeced sheep farming, cultivation of industrial crops, irrigation, and forestry) and contributed into the development of the region as a whole. Cornies also implemented social projects, reformed education, was interested in the development of scientific knowledge. Johann Cornies was not a part of the bureaucratic system of the administrative vertical in the Empire, but he was a kind of link that connected the vertical with economic structures at the local level. The Cornies’ phenomenon was a manifestation of the closed Protestant congregations’ under the conditions of colonization development, when they needed for economic adaptation and the preservation of their ideological identity. Mennonite society, which had traditions of religious isolation, could not perceive the leader imposed by the authorities. However, the congregations also needed the kind of personalities as Cornies was. He was a leader from their own environment, with “broad optics” of view, ideological breakthrough ability and analytical skills. In a general retrospective of the analysis of the economic development of settlements, the phenomenon of Cornies’ activity confirms that Mennonite society had the ability to self-reform, which provided them with a high position in the modernization processes of the Russian Empire. Practical value: can be used for synthesis works on the problems of colonization and Protestantism in the Southern West of the Russian Empire. Novelty. The image of the leader of the Protestant type in the Mennonite colonies was created. Type of article: theoretical and analytical.