I'm looking for the largest territory (by population) which satisfies the following criteria:
- A single person has all the decision making power in their hands, constrained only by whatever powers are delegated to said territory from a higher level of government. I.e. a mayor of a city that doesn't have a city council or where the mayor can completely ignore the city council if they so desire.
- Said person is elected democratically (directly or indirectly) in an election where the majority of the territory's residents can participate. So positions such as Saudi Arabia's King are excluded.
- The powers of said person can be executed de facto, not de jure. So the British Queen wouldn't count even if it was an elected position, as she doesn't exercise any of her powers directly these days.
- If no such notable positions exist these days, historical positions from within the past 100 years would count too.
Largest example that I'm aware of is Bartow County, Georgia, with a population of 107,738:
It has a sole commissioner government, and is the largest county by population of the few remaining in Georgia with a sole commissioner.