The article discusses the units of Mari origin in the toponymy of the Nizhny Nivgorod region and in the microtoponymy of the right bank, Oka-Volga-Sura interfluve area, alongside multilingual proper names. Microtoponymy is also analyzed from the perspective of communicative dialectology and communicative onomastics. Special attention is paid to analyzing onymic items (toponyms: hydronyms, place-names; micro-toponyms) from the point of view of regional and dialectic systems, i. e. by the reinhabitants of the regions, focusing on discourse texts as component parts of micro-toponymic complexes. Ethnic motivation, in its turn, involves hypothetical assessment of names – starting from the most generalized, such as: “non-Russian” or “vrode (“some”) non-Russian”, to a more concrete one – “vrode (“chay”, “navernoye”, “podi” (meaning “may be”) Mordovian (Tatar)”, “Mordovian or Tatar”. Internal information with the status of folk etymology, allusions, up to clear fantasies, are considered to be ethnically, historically and demographically significant, since they generally express the awareness of multiethnic population of the region in the past. The territorial assessment of Mari onymic lexical layer units (topolexems, topoformants) as general indication of Nizhny Novgorod region areas: “Levoberezhye” (left bank area) – “Pravoberezhye” (right bank area) is pointed out. Etymological multi-versioning (outside the system) in scientific interpretation of the origin of toponymic units is also touched upon (with Mari and Mordovian etyma) and with generalized ethnic explanations like “derived from Finno-Ugrian…”, “of Finno-Ugrian origin…”. The conclusion is about the size and importance of Mari (and Mari-Mordovian) toponymic layer including in the historical and cultural area of Oka-Volga-Sura interfluve, which is indicative of historic, ethnic and demographic processes in the region.