| Name | Country | 14C dates | |
|---|---|---|---|
|
321-340 / 936 show all | |||
| Osjecko-Baranjska | Croatia | 2 | Show |
| Oromiya | Ethiopia | 4 | Show |
| Orne | France | 48 | Show |
| Orkney | United Kingdom | 94 | Show |
| Oristrano | Italy | 2 | Show |
| Orenburg | Russia | 9 | Show |
| Orebro | Sweden | 32 | Show |
| Opole | Poland | 47 | Show |
| Oplotnica | Slovenia | 0 | Show |
| Omagh | United Kingdom | 25 | Show |
| Olt | Romania | 0 | Show |
| Olomoucký | Czechia | 44 | Show |
| Oldham | United Kingdom | 5 | Show |
| Oise | France | 56 | Show |
| Offaly | Ireland | 16 | Show |
| Odessa | Ukraine | 50 | Show |
| Ocniţa | Moldova | 2 | Show |
| Obwalden | Switzerland | 5 | Show |
| Oberösterreich | Austria | 9 | Show |
| Nuoro | Italy | 11 | Show |
