The government legislation that defines the R377, the Roads Act 1993 (Classification of Regional Roads) Order 2012 (Statutory Instrument 54 of 2012), provides the following official description:
R377: Castleplunket — Castlerea, County Roscommon
Between its junction with R367 at Castleplunket and its junction with N60 at Saint Patrick Street Castlerea via Lissalway, Ballinphuill, Knockmurry; and Main Street at Castlerea all in the county of Roscommon.[1]