Geo.country

The country as an ISO 3166-1 alpha-3 code, three uppercase letters such as "USA", "GBR", or "DEU".

CurrentstringOptionalSince 2.0

Field facts

Buyers use it for campaign geography and often to decide which privacy regime applies, alongside regs.gdpr and regs.gpp_sid.

Where the field sits in a payload, with everything else left out:

{
  "id": "req-1",
  "device": {
    "geo": {
      "country": "USA"
    }
  }
}

Sending the two-letter code ("US") instead of three letters. Buyers matching on alpha-3 miss the country entirely.
Sending a country name or lowercase code.

Added in OpenRTB 2.0, and present in the latest snapshot. The table shows how each version's spec text types the field.

Versions	Type in the spec	Required	Deprecated
2.0 to 2.2	string	No	No
2.3 to 2.3.1	string	No	No
2.4	string	No	No
2.5 to 2.6-202606	string	No	No