Troitsk (; , Trojtsä) is a rural locality (a selo) in Kovylkinsky District of the Republic of Mordovia, Russia.
Troitsk was founded in the 17th century as a fortress. During the Stepan Razin rebellion, Troitsk was a rebels' stronghold. From 1780 to 1798 Troitsk was an uyezd center of the Penza Governorate, after which it became a supernumerary town in Krasnoslobodsky Uyezd, ultimately losing town status in 1925.
Population: 5,822 (1897 Census).