As with other things, quality matters more than quantity. A village elder or city mayor are just as fallible as a parliament, or a king and his council. The mechanism of corruption may vary with historical circumstance, culture, and/or technology. But at the end of the day, if the "people in charge" are unaccountable and have no desire to exercise their power for the common good, there is no system of checks and balances that will save such a government from collapse.