The BBC has this article about Brighton, England, which has a city council controlled by the Green Party. Brighton, on the south coast of England, has a population of 273,400, and is probably the largest jurisdiction in the English-speaking world where the Green Party is the dominant force in government.
The city council has 54 members, consisting of 21 Greens, 18 Conservative Party members, 14 Labour Party members, and one independent. Brighton also has the nation’s only Green Party member of the House of Commons, Caroline Lucas. Thanks to Thomas Jones for the link.