The Sangamon Mass Transit District (SMTD) is a regional mass transit district that mostly serves Springfield, Illinois along with a few neighboring communities. It is governed by a seven-member board of trustees, who are all appointed by the Sangamon County Board of Supervisors. In 2023, the system had a ridership of 1,406,900, or about 4,900 per weekday as of the fourth quarter of 2023.

Sangamon County is a county located in the center of the U.S. state of Illinois. According to the 2020 census, it had a population of 196,343. Its county seat and largest city is Springfield, the state capital.