Deep in a cave on a hill, in Udayagiri in Vidisha, Madhya Pradesh, archaeologists found a 5th century CE, Gupta era sculpture which they believe could be the oldest dateable representation of the elephant god, Ganesha.
Udayagiri caves are a complex of almost twenty Hindu and Jain caves dating back to the Gupta period. This complex of caves contains a spectacular array of images including those of Vishnu in the Varaha or boar avatar lifting Bhudevi, the earth goddess. But of greatest interest to historians is Cave no. 6, where you can see the image of a portly Ganesha with the matrikas or mother goddesses next to him. This very famous Udayagiri Ganesha is considered the oldest representation of the elephant god in the country!
But like always, views on this differ. Take a seven hour drive to village of Bhumara in Satna district, also in Madhya Pradesh and you will find another sculpture of Ganesha at the Bhumara Shiva temple. Given that both the sculptures are from the same late Gupta period, one really can't be sure which came first.
This is not to say that older images of elephants have not been found. There are elephant seals dating back to Harappan times but there are no traces of them being worshipped.
Elephant as an icon is also found in coins of Indo-Greek kings such as Menander and Demetrios. A coin of Demetrios I (r. c.200-180 BCE) shows him wearing an elephant headdress to mark his Indian conquests. Elephants also appear in Buddhist sculptures at the Bharhut stupa in Madhya Pradesh dated to 100 BCE.
Historians like Dr M K Dhavalikar believe that actual worship of Ganesha began only in the later days of the Gupta period between 450 -500 CE - the time when the Udayagiri and Bhumara temples were made.
In more recent times, the man who took Ganesha to every home was freedom fighter, Lokmanya Tilak. He is credited with reviving the Ganesha Utsav in the 1890s. This helped transform a local, low key Maharashtrian celebration into the mega festival it has become today!