This is a very subjective question. It highly depends on what you would define as city centre. Nevertheless: Tallinn Lennart Meri airport is serving Tallinn and only 4.3km from Tammsaare Park in downtown Tallinn.

There is perhaps a question whether we count driving distance or straight-line. BOS is a good candidate if the latter.

What about Midway Airport in Chicago, Il, USA?

Gibraltar Airport is 2.1km from the city center to the passenger terminal; however, it has only 33,000+ people and thus falls short of the guideline.

You should probably exclude heliports. The distance from the Downtown Manhattan Heliport to the New York Stock Exchange is about 650 yards.

Really, the question is "what counts as the city center"?

Probably another rule should be that the airport has significant commercial service. Some cities have "downtown airports" that are used for private aviation only, e.g. MKC.

See also: travel.stackexchange.com/questions/74629/… (closed as too broad)

What about Santos Dumont airport in Rio de Janeiro? You can walk out from the airport and right into the downtown.

Don't have enough reputation to post an answer, but Fukuoka's airport is inside the city. The city's population is 1.5 million.

VTC as unclear because "city center" is ill-defined and I am sick of this sort of silly questions. Whatever happened to "You should only ask practical, answerable questions based on actual problems that you face."?

Tons of European cities and towns have airports within city limits and — arguably — next to the city centre (if by “next to” you include being able to take regular public transport or even walk just): Berlin (2×), Lisbon, Geneva, Cambridge, London … just off the top of my head.

London City airport is a km or so east of the Greenwich meridian, and so for a dodgy meaning of 'center' is very near the center of London.

The Aeroporto Capodichino in Naples (Italy) is a 3.8km drive from the city centre according to Google Maps (if we count the Piazza Giuseppe Garibaldi as the city centre).

I don't have rep to answer, but Cuenca, Ecuador is probably a top contender. The SW end of the runway is closer to downtown than it is to the NE end of the runway.

@GrzegorzOledzki The question is protected. You need 10 rep (on travel, specifically - association bonus doesn't count) to answer a protected question.

Why wouldn’t city centre be well-defined? Cities usually have a specific point that is used to calculate the distance on traffic signs, why not take that?

@11684 in the US, at least, this concept seems to be tenuous at best. I always thought it was actually measured to the city boundary, but a little research found a sign on I-95 in Connecticut claiming 47 miles to the city, as well as a separate claim that the distances are measured from Columbus Circle. The sign is much closer than that to the boundary, but every route I could map to CC was over 50 miles, including on foot, which I presume to be more direct. It's a bit of a mystery, actually.

This is definitely not too broad. City centres are well defined - if you want a specific point, just use google maps: every city has a point defined. Voting to reopen!