How many Green Lanterns are there?

And how many are there in each other corps?

Around 7200 members stationed in about 3600 sectors for Green Lanterns. Don't know much about the others though.

Orange Lanterns = 1

It varies, but as far as we know there is less than 7200 in each corp right now. Most have under 100.

I think there's only about 6 in the Red Lanterns as of issue 21.

7200 green lanterns with Kilowog being the greatest of them all.

there are more than 7200 Green Lanterns....those are only the Sector Lanterns....there are still the Honor Guard Lanterns like Kyle Rayner, Guy Gardner, Kilowog, and others...plus all of the Lanterns who are regularly stationed on Oa for maintenance and other jobs there

I thought most of the ones stationed in Oa such as Wog also had sectors to patrol. Maybe not the cook or Morrow but overall it shouldn't be much more than 7200.