With the formation of the Kazan and Ufa provinces in the early eighteenth century by Tsar Peter I, these provinces delineated the border of the Kazan diocese. Through the remainder of the century, the borders varied, especially during the reforms of Tsarina Catherine II. By the 1790s the diocese was defined by the reorganized Kazan and Simbirsk provinces that were established in 1789. Then, after the creation of Simbirsk diocese in 1832, the Kazan diocese included only the territory of Kazan province.
After the formation of the Soviet state, borders of Kazan diocese were adjusted to the new territorial organization. In the 1920s, the diocese included
the the Chuvash and Mari republics in addition to that of Kazan. In 1946, the Cheboksary and Mari dioceses were formed, followed in 1993 by the formation of the Yoshkar-Ola and Mari diocese. With these changes the borders of the Kazan diocese coincided with those of Tatarstan.