You will need some history of the zoning. Look at the former property owners and the zoning for them. Then check the archives for any mention of zoning changes. Changes require a public notice, a public hearing and a legitimate vote of the officials in order to be legal.
Get archive copies of the local paper if you can. A lot of change proposals are listed in the paper.
Get archive copies of the local paper if you can. A lot of change proposals are listed in the paper.