Proud Brooklynites (and is there really any other kind, lol?) can argue that NYC’s current Mayor Eric Adams is a native of Brooklyn, and more than a few Hizzoners have hailed from Kings County…
But there was a time when all the Mayors of Brooklyn were from, well, Brooklyn!

While the City of Brooklyn is not within living memory (1898!), the days of a September Mayoral Primary Day is something many New Yorkers experienced. September Mayoral primaries ended when ranked choice was approved by a referendum held during the November 5, 2019 general election (L.L. 215/2019).
And to explore more about NYC’s most populous borough, and how it ceased to be a city… I recommend you take a peek at one of NYLI’s eBooks…
And for a closer legal look at all of New York Election law — consider borrowing ….
For Election Law information… charter & codes (current & superseded) … and really, any legal materials – consider joining The New York Law Institute for access…