Alaincourt (French pronunciation: [alɛ̃kuʁ]) is a commune in the department of Aisne in the Hauts-de-France region of northern France.

The Motorway from Saint-Quentin – the E17 (A26) – passes directly through the commune heading south-east towards Reims – some 120 km to the south-east.

The motorway has no exit in the commune so it must be reached by the road D34 coming north-east from Moy-de-l'Aisne and continuing north-east to Berthenicourt.

East of the village the commune is traversed by the Oise river and the Canal de la Sambre a l'Oise both waterways heading south more-or-less parallel to each other (the canal in a straight line) until the Oise joins the Aisne at Clairoix and continues as the Oise until it joins the Seine at Conflans-Sainte-Honorine in the north-west of Paris.

There are a number of ponds and reservoirs near the Oise in the south-east of the commune.