Population of O'Neill cylinder

> The 10 million number was an estimate if the cylinder was occupied to
> the same density as a proposed island one cylinder.

Assuming you're talking about the model 4s...

Assuming outer 1% of the 6.5km diameter has an acceptable gravity, you could
effectively have a tower block ~20 stories tall, and 20km long. My two
person flat is 7m long, so ~3000 could fit on each level, with a total
population of 3000*20*2 per end cap. With 4 end caps in a colony this give
you a population of about half a million. Total land area is 650 million
square meters - in each cylinder. Taking my block of flats as a model, and
extending it to 20 floors, the remaining 9.5M people would occupy 12.6M
square meters of land, with each tower block basically having two square
miles of 'garden'. Which is about 0.01% of the total area of both cylinders.

You can more than easily fit 10 million in. If you want to.

John