Azure Cosmos DB is present across all Azure regions, as specified on the Azure regions page. Because it's the core service, every new datacenter has an Azure Cosmos DB presence.
When you set a region, remember that Azure Cosmos DB respects sovereign and government clouds. That is, if you create an account in a sovereign region, you can't replicate out of that sovereign region. Similarly, you can't enable replication into other sovereign locations from an outside account.