Barby is located immediately north-west of Rethel and immediately south-east of Château-Porcien.
Access to the commune is by the D926 road from Rethel which passes through the heart of the commune and the village before continuing north-west to Château-Porcien.
The D946 from Rethel passes through the north of the commune as it goes north-west to Seraincourt.
The commune is entirely farmland.

The Aisne river passes through the south-east of the commune forming a small part of the south-eastern border as it flows west to eventually join the Oise at Compiègne.
The Vaux river flows south, forming the western border of the commune, to join the Aisne just outside the south-western tip of the commune.
The Ruisseau de Bourgeron flows from the north-east through the commune and the village and joins the Aisne on the southern border.
The Canal des Ardennes is parallel to and south of the Aisne and forms a small portion of the southern border of the commune.
Barby is located immediately north-west of Rethel and immediately south-east of Château-Porcien. Access to the commune is by the D926 road from Rethel which passes through the heart of the commune and the village before continuing north-west to Château-Porcien. The D946 from Rethel passes through the north of the commune as it goes north-west to Seraincourt. The commune is entirely farmland.
The Aisne river passes through the south-east of the commune forming a small part of the south-eastern border as it flows west to eventually join the Oise at Compiègne. The Vaux river flows south, forming the western border of the commune, to join the Aisne just outside the south-western tip of the commune. The Ruisseau de Bourgeron flows from the north-east through the commune and the village and joins the Aisne on the southern border. The Canal des Ardennes is parallel to and south of the Aisne and forms a small portion of the southern border of the commune.
Barby, Ardennes