Route 37A no longer exists. In 1934, it was created in New Fairfield and Danbury, inheriting most of its route from the short-lived Route 100. The alignment of Route 37A, 8.52 miles long, from south to north:
- Today's Route 39, from Route 37 in Danbury to Warwick Road in New Fairfield
- Warwick Road, continuing to Pembroke Road (Route 37)
The section of Ball Pond Road between Milltown Road and Warwick Road was an overlap with the comtemprary Route 39.
In 1963, Route 39 was relocated from Milltown Road to its modern routing into Danbury. Warwick road was turned over to the town, and Route 37A disappeared.