Q & A: Real estate purchase and zoning laws: can the township authority make me do this?

Q: My mom has some acreage (not much, actually, less than ten acres). She wants to sell me a parcel of her property so that I can build on it. I live in a crummy area, there's a lot of drug dealers around me. I want to build on that land I'm buying from my mom, and bring my kids to that school district too, which is better for everyone. The land has always been in our family, and probably always will be. The problem is that it is zoned agricultural. I have also heard that the township won't let land be parceled smaller than 8 acres in that area. Can the township authority do that, stop me from building because it's zoning it that way? Can they stop my mom from selling to me based on the size of the parcel?

A: Probably, the township authority can do that. 
Your questions center on the area of real estate law, specifically zoning, and the validity of zoning laws.
The thing is that governments (in this case, the township authority) is not supposed to interfere with property rights. Property rights loosely means you can use your property (the land your mom wants to sell you will become yours) however you want to use it. This right to use the property usually applies to how it is sold, legally this is referred to as making property "freely alienable," or easily sold, given away, etc. Governments are not supposed to do things that make it hard for you to use or sell your property.

However, since the area is zoned agriculturally, it may present a barrier. The problem is that the zoning law is usually upheld - this means that townships like yours can (usually) show that there's a community interest in keeping things the way they are - if it is zoned as agricultural, it may have to stay agricultural. That is, unless, you can show (through an appeal to the zoning board before the property is sold to you) that the continuance of zoning is unreasonable because there is no possible way for the property to continue as agricultural use.  The best fact you have going for you in this scenario is that the parcel she has already is sort of small (for agricultural use), but does that mean that it wouldn't ever be useful as agricultural again? That's what a zoning board of appeals would have to decide.