Azy-sur-Marne is located 4 km south-west of Chateau-Thierry and 20 km east of Montreuil-aux-Lions. It can be accessed by the D969 road from Essomes-sur-Marne in the north through the village then west through the commune and continuing south to Romeny-sur-Marne. There is also a country road going west to Mont de Bonneil. The commune is almost entirely farmland with small forests in the north and west. The commune is within the Appellation d'origine contrôlée zone of Champagne of Aisne.
The southern border of the commune consists of the Marne river with no other identifiable watercourses in the commune.
In 2010, the commune had 387 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.