Avançon is located some 10 km south-west of Rethel and 11 km east of Asfeld. Access to the commune is by the D18 road from Acy-Romance in the north-east which passes through the commune to the village near the centre then continues west to Blanzy-la-Salonnaise. The D26 road goes from the village north to Taizy. The D150 goes south-west from the village to Saint-Loup-en-Champagne. The commune is entirely farmland.
In 2010 the commune had 328 inhabitants. The evolution of the number of inhabitants is known from 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 communes 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" allows, after a transitional period running from 2004 to 2008, the annual publication of the legal population of the different French administrative districts. For communes with a population greater than 10,000 inhabitants, a sample survey is conducted annually, the entire territory of these communes 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 on 1 January 2009 and was based on the census of 2006.