Status: Active as of June 17th, 2021
The Region ID is a dimension in Google Analytics under the Audience > Geo section.
The Region ID represents the users' region, derived from their IP addresses or Geographical IDs. Depending on the country, the Region ID might represent any one of the following region types: State, Province, Prefecture, Region, Union Territory, Autonomous Community, County, Canton, Governorate, Municipality, Department, District, or Territory. A Region might have one or more City IDs within it.