Route 309 is a Connecticut state highway in the northwestern Hartford suburbs running from Canton to Simsbury.

Route 309 begins at an intersection with Route 179 in North Canton and heads southeast into Simsbury. In Simsbury, it curves southeast and east to end at an intersection with Route 167.

North Canton Road and West Simsbury Road was established as SR 909 in 1962 as part of the Route Reclassification Act. The following year, SR 909 became a signed route, with the designation Route 309.

The entire route is in Hartford County.

Location	mi	km	Destinations	Notes
Canton	0.00	0.00	Route 179 – Collinsville, Barkhamsted	Western terminus of CT 309
Simsbury	4.74	7.63	Route 167 – Avon, Simsbury Center	Eastern terminus of CT 309
1.000 mi = 1.609 km; 1.000 km = 0.621 mi