This page will provide information about where the O-2As are and what they are doing. For those visitors who own and fly an O-2, please contact me to share some information about your plane and what you do with it.
Somewhat more than 20 are on static display at various museums across the United States
That leaves about 200 airframes to account for. Of those:
5 are registered in other countries, 3 in Australia (and "good on 'em" as there were Australian O-2 FAC's in the SEA conflict) two in Canada (not counting N-registered airplanes that happen to live in Canada), one in the Czech Republic, and one is a recent arrival to the Netherlands (I had the pleasure of meeting the owner/pilot at Airventure 2013.)
There are 82 aircraft registered by the FAA as either O-2A or M337B (Cessna’s designation for the Military variant of the C-337B). Of those, 20 registrations have expired, leaving 62. That number is imprecise. Some of the expired registrations are due to the FAA being less than speedy in processing the registration renewals required every three years. Other aircraft may have current registrations, but are not flying or airworthy, the owner keeping up the registration in the hope that it will someday fly again. Altogether, estimates are that there are less than 50 O-2As flying (and only one O-2B.) That O-2B came to Oshkosh this year (2021), N446TF/Ser#67-21446. It is owned by a retired USN CAPT and looks beautiful.
So where are they? What are they doing? What happened to the other hundred?
Here is a quick update as of October 12 2014. With some help from contributors to this website and deep diving into the FAA records, I have some numbers for 1967 (the year 424 was delivered)
There were 146 O-2A's delivered in 1967, of these:
55 were lost in Southeast Asia: 32 were shot down, 13 were other combat losses (like getting hit by artillery on the ground); 10 were lost due to accidents or mishaps
28 are in the FAA registry: 17 have current registrations and airworthiness certificates; 11 either have no airworthiness certificate on file or have expired registrations
10 are in Museums.
3 to foreign military sales
3 are on the Australian civil registry
2 are on the Canadian civil registry
If my math is right that leaves 45 with whereabouts unknown. The search continues...