What was the US Supreme Court case Munn v. Illinois about?

Munn v. Illinois, 94 US 113 (1877)

The question that the case was concerned with was whether a state could regulate charges for grain elevators. This is expanded - using the idea that a state has the right to regulate commerce within that state - to the fact that if a private utility is used in the public good, it should be regulated by the state, as the state is acting on behalf of the people's interest.

Granger laws were legal...Apex...:)