In Hollywood Westerns, the lawman strides authoritatively into the saloon, and the gamblers at the table, the seductress at the bar and the bad guy sulking in the corner variously address him as "Marshal" or Sheriff." Both are terms that mean "lawman," but they weren't any more synonymous in the Old West than they are today. Stars, guns and white hats notwithstanding, marshals and sheriffs had different functions and different realms of authority.
There is in fact, a very distinct difference that I was never aware of.
"The more you know"