Barenton-sur-Serre is located some 35 km south-east of Saint-Quentin and 15 km north-east of Laon. National Route N2 passes through the commune from Froidmont-Cohartille in the north-east running south-west through the commune. Access to the village is by road D3060 running west from the N2 to the village then continuing north-west to road D12. There is also access to the village on a country road from Froidmont-Cohartille. There is quite a large area of forest north of the village and in a belt extending south-east of the village. The rest of the commune is all farmland.
The Ru de Barentons flows from the south of the commune into the Souche river which flows from east to west through the commune then continues north-west to join the Serre river.
In 2010, the commune had 115 inhabitants. The evolution of the number of inhabitants is known through the population censuses conducted in the commune since 1793. From the 21st century, a census of municipalities with fewer than 10,000 inhabitants is held every five years, unlike larger towns that have a sample survey every year.[Note 1]
^At the beginning of the 21st century, the methods of identification have been modified by law No. 2002-276 of 27 February 2002 , the so-called "law of local democracy" and in particular Title V "census operations" which allow, after a transitional period running from 2004 to 2008, the annual publication of the legal population of the different French administrative districts. For municipalities with a population greater than 10,000 inhabitants, a sample survey is conducted annually, the entire territory of these municipalities is taken into account at the end of the period of five years. The first "legal population" after 1999 under this new law came into force in 1 January 2009 and was based on the census of 2006.