Route 189 is a state route in the U.S. states of Connecticut and Massachusetts. The route begins in the northwestern portion of the Connecticut state capital of Hartford and ends in the rural town of Granville. In Massachusetts, the route is not a state highway and is maintained by the town of Granville.

Route 189 begins at an intersection with US 44 in western Hartford and heads northwest, crossing into West Hartford. It continues northwest across the northeastern corner of West Hartford and crosses into Bloomfield. In Bloomfield, it continues north, with two northwest jogs, through the town before a brief freeway segment heading northwest along the Farmington River, overlapping Route 187 for part of the freeway. After the freeway, it continues northwest into Simsbury. In Simsbury, it continues north along the Farmington River before crossing the river into East Granby. In East Granby, it continues northwest to Granby. In Granby, it continues northwest, briefly overlapping US 202 and Route 10, immediately followed by a brief overlap with Route 20. It then continues northwest across the town to the Massachusetts state line, where it continues north towards the town center of Granville, ending at an intersection with Route 57.

The route from Granby center northwest through North Granby to the Massachusetts state line was designated in 1922 as State Highway 206. In the 1932 state highway renumbering, Route 189 was established as a new designation for old Highway 206. It originally ran from Route 20 in Granby to the state line. At the same time, Massachusetts designated the continuation as Route 189 in Granville to Route 57. The portion south of Route 20 was, at the time, designated as part of Route 9. Before 1932, this portion was still part of New England Route 10. The original Route 9 in Bloomfield followed Tunxis Avenue into Tariffville before continuing north along Hartford Avenue, crossing the Farmington River three times in the process. In 1960, five years after two of the bridges were washed out in a flood, Route 9 was relocated to stay on the south side of the river along a newly-built expressway. In 1963, with the opening of the Route 9 freeway south of Hartford, the section of Route 9 from US 44 in Hartford to Route 20 in Granby was reassigned as a southern extension of Route 189.