Objects belonging to a bucket that you create in a specific AWS Region never leave that region, unless you explicitly transfer them to another region. For example, objects stored in the EU (Ireland) region never leave it.

Creating a Bucket
Accessing a Bucket
Bucket Configuration Options
Bucket Restrictions and Limitations
Examples of Creating a Bucket
Deleting or Emptying a Bucket
Amazon S3 Default Encryption for S3 Buckets