The place: The United States of America.
The time: Whenever organised crime bosses think that they could have a chance of succeeding, between the English recognition of the US as an independent nation and now.
The goal: Organised crime figures to openly usurp government in a minimum of one entire US state, though preferably all of the USA.
I would consider government to have been usurped by organised crime if:
The majority of the police have been bought, intimidated and/or killed such that they can no longer effectively even attempt to suppress organised crime other than as directed by the organised crime government.
No effective intervention by military forces based in the controlled area is possible. This does not include the possibility of intervention by external military forces.
Organised crime figures are openly in charge, and public revelation of their crimes can have no immediate negative consequences to them. I.e. they need make no pretence at being virtuous.
The organised crime government need not make any pretence at following state or federal constitutions, and may use whatever means they want to add, remove or replace members of their government that they want.
The usurpation of government may take place by any feasible means, so long as it becomes apparent that the former constitutional government is no longer in effect.
The change of government must persist for a minimum of one year, preferably longer.
The organised crime figures who rise to usurp government may be real historical figures or may be plausible fictional characters.
Is this possible? If so, how? If not, how close could the USA come to having it occur?