Where was the metric system developed?
Most historians agree that Gabriel Mouton, the vicar of St. Paul's Church in Lyons, France, is the "founding father" of the metric system. Therefore, I have to say Lyons, France.
The metric system is a system of units for measurement developed in late 18th century in France.It was developed by the chemist Lavoisier to replace the disparate systems of measures then in use with a unified, natural and universal system. In the early metric system there were several fundamental or base units, the meter for length, the gram for weight and the liter for capacity.
The measure metre was always metric. A few philosophers and scientists had proposed a decimal system earlier, but in 1790 the National Assembly of France asked the French Academy of Sciences to invent a standard system of weights and measures. The system they developed became the metric system and it was adopted by the French government in 1795.