The article deals with the functioning of proper names (both personal and place names) and their derivatives in dialectal idioms. Based upon the criteria of the establishing of the idiomatic status of word combinations, traditionally used in contemporary lexicology, the author marks out four stages of the entry of units containing proper names and their derivatives into a regional idiomatic inventory: 1) word combinations with figurative meanings and transparent motivation easily decoded by every member of the local community (e. g., naryaditsa kak Anisya Klimovskaya ‘to be slovenly dressed’); 2) word combinations with a proper name localizing a nationally known idiom (e. g., zhelninsky telyonok ‘screaming person’); 3) word combinations including a name with a general meaning (e. g., Masha s Yashey ‘two inseparable persons’); 4) idioms with non-transparent motivation (e. g., tutursky pop ‘cuckoo male’). The analyzed data are retrieved from dialect dictionaries (including those of idioms) and notes made by the Ural Federal University Toponymic Expeditions in Kostroma Region in 2011-2013.