Agnin is located some 25 km south of Vienne and 5 km north-east of Saint-Rambert-d'Albon. It can be accessed by the road D519 from near Chanas in the west passing through the southern part of the commune and continuing to Bouge-Chambalud. Parallel to this road in the north of the commune is the D51 road from Salaise-sur-Sanne in the west passing through the commune and the village and continuing to Anjou in the east. The D131 also comes from the Ville-sous-Anjou in the north joining the D51 west of the village. The Route de Bouge connects the village to the D519 in the south of the commune. The commune is mostly farmland with significant areas of housing in the north and some small areas of forest in the south.
An unnamed stream flows south forming the western border of the commune and another unnamed stream flows through the commune then forms the south-western border. They both join in the south-west and continue flowing west. The Dolon stream forms the southern border of the commune
Like the nearby town of Anjou the origin of the name Agnin comes from the name of a Roman noble Anianus who owned vast territory in that era. The name of the town changed a few centuries later to Agnino which was the name used in the 11th century to describe this commune. Then over the following centuries Agnino became the Agnin known today.
Blazon: Party per bend sinister, one of Or a local church soutenu at dexter by an inescutcheon with two keys saltirewise and sinister in chief a Vol all represented in lines; two of gules a dolphin of Or at dexter and a rose gules stalked and leaved in vert; in the cotice a bend sinister in Or charged with the letters AGNIN in sable debruised on the division.
In 2009, the commune had 969 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.