Can anyone confirm when Auxerre has its farmer's market day(s)?

no, but 1) the concept of Farmer's market is an American one, market is enough and FM will confuse. 2) https://www.ot-auxerre.com just drop these guys a line, they will be able to read English.

Hi,
According to the city website, it seems there are several ones:
- Tuesday & Friday morning, Place de l'Arquebuse
- Wednesday, in the center of the city
- Sunday, Place Degas

However, the most interesting one is probably on Saturday morning, in the center of the city (close to the city hall): this is a local producer market

A quick extra tip if you are interested in wine: you are in the area of Chablis. The village is only 20km (12mi) from Auxerre. There, I recommend you the wine merchant "La Chablisienne". Very good one, and you can pick the "Chateau Grenouilles", one of my favorite in this region. Maybe you will also find them at the market, on Saturday.

My favorite Coop Tom, nice people

The area also has Auxerre wine and the AC of Irancy to the south and even a Sauvignon Blanc AC to the south (not great but interesting)

Thanks for the response! I did finally research further and learned of the Tuesday market, which interests me the most. Cheers!