Depends what you call a concert. Every summer here, we have free musical events in a large central city park. According to the reviews, and according to who you believe, and how they do their count, the attendance is about 250 000 people.
But the people haven't come for the music. They've come for a picnic, to chat with their friends, have a wine or 2 or 3, and to see the fireworks that go with the "1812". Everyone has a good time, and arrests are only about 2 or 3 out of all those people, but I wouldn't call it a concert.
If I did, I could say that 25% of this region's population have attended a classical concert in the last 12 months.
Luckily, the music is well amplified, through quite a good speaker system, so if there's not too much wind, those of us who actually like the music can hear it.
Omnia me Graeci est.