Les Alleux is located some 30 km east of Rethel and 10 km north of Vouziers. The commune can be accessed by the D977 road from Vouziers in the south passing through the commune to the east of the village and continuing to Le Chesne in the north. Access to the village is by the D23 road from Voncq in the west and continuing north to join the D977 inside the commune. Most of the east and west of the commune are forested with the central part farmland.
An unnamed stream rises south of the village and flows north-west to join the Ruisseau des Graquinettes just west of the commune.
In 2009, the commune had 84 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 communes 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.