Councillor Pete Smith said he was concerned there was a 'hidden agenda' with the event.
He believes it could end up with one council being formed to cover the entire Black Country - which he says would be bad for the area.
Dozens of events across the whole area pulled in huge crowds over the weekend as local celebrities helped mark a celebration of what makes the region's towns great.
But Councillor Smith says he does not believe the concept of the Black Country has an relevance in today's society.
The Democratic Labour councillor said: "I have got some serious reservations about this and I think there could be a hidden agenda.
"I'm a bit worried that there is someone in a back room looking at how this can lead to a council for the Black Country area.
"I'm not too keen about the actual description 'Black Country'. I know it dates back to the industrial days but I don't know how relevant it is now.
"I am raising this as a concerned local councillor rather than as the Mayor of Walsall."
Thousands of people celebrated Black Country Day yesterday.