NY 121 begins at a junction with
NY 22 (Cantitoe Street) in the
hamlet of
Bedford Village, just north of the junction with
NY 172. The route proceeds northeast out of Bedford Village, crossing through the town of
Bedford and over the Stone Hill River. Winding northeast and soon north through the dense woodlands of Bedford, NY 121 reaches a junction with the northern terminus of
NY 137 (Stone Hill Road). The route winds north through Bedford as a two-lane road past Pea Pond before reaching the southern end of the
Cross River Reservoir. Just after the junction with Upper Hook Road, NY 121 crosses over the southern extremities of the reservoir, crossing into the town of
Pound Ridge. Now in Pound Ridge, NY 121 runs along a small branch of the Cross River Reservoir, crossing into the town of
Lewisboro and gaining the moniker of Cross River Road. The route soon enters the hamlet of
Cross River, where it meets the
namesake river, reaching a junction with
NY 35. NY 35 and NY 121 become concurrent, crossing northeast through the hamlet before reaching Cross River Plaza, where the routes fork. Leaving Cross River, NY 121 continues north through Lewisboro, returning to the dense woodlands. After passing west of Waccabuc, the route reaches a junction with the terminus of
NY 138 just before crossing the town line from Lewisboro into
North Salem. NY 121 winds northeast through North Salem, gaining the moniker of Grant Road, soon reaching the hamlet of Grant Corner. Here, the route intersects with June Road (unsigned
County Route 310 or CR 310). Beginning a parallel with the
Titicus River, NY 121 soon reaches a junction with
NY 116, which become concurrent as NY 121 bypasses the hamlet of North Salem. At the junction with Peach Lake Road, NY 116 continues east on Titicus Road while NY 121 turns north on Peach Lake. Continuing north through North Salem, NY 121 begins running to the east of Peach Lake, retaining the Peach Lake Road name until reaching the
Putnam County line in the hamlet of
Peach Lake. Now in the town of
Southeast, NY 121 runs alongside the Vail's Grove Golf Course and soon into exit 69, a pair of ramps from
I-84. Just north of the I-84 interchange, NY 121 terminates at an intersection with
US 6 and
US 202 in front of the
East Branch Reservoir. ==History==