Route 243 begins in the Westville neighborhood of New Haven as Fountain Street branching from Whalley Avenue (
Route 63 towards the west, while Whalley Avenue continues northwest). Fountain Street passes by the Westville Post Office then continues through the residential part of Westville. Along the way, it intersects
Route 122 (Forest Road and Dayton Street). Fountain Street continues west, going under the
Wilbur Cross Parkway (does not have an interchange with it) into the town of
Woodbridge. Within Woodbridge, it intersects with Woodfield Road, which provides access to the Woodbridge Country Club.
Route 313 (Rimmon Road) begins near the country club, heading directly for the town of
Seymour. After the junction with Route 313, the road changes name to Ansonia Road. About later, it intersects with
Route 114 (Racebrook Road), which leads to
Orange (south) and Woodbridge center (north). Route 243 then enters the city of
Ansonia, just north of the
Derby city line. Within Ansonia, the road becomes known as Pulaski Highway. At the end of the road, Route 243 then turns left on Prindle Avenue, right on Platt Street, and left on Elm Street, finally ending at
Route 115 (Main Street), south of downtown Ansonia near the Derby line. Across Main Street, the road becomes Division Street, an unsigned state highway connector across the
Naugatuck River that connects to Pershing Drive (SR 727) in Derby. Division Street has the unsigned designation SR 853. ==History==