Yep, it's a different, wider (geographically) group, but also more narrowly focused on the TK costume.
Here's the breakdown:
The 501st Legion (501st.com) is the world-wide umbrella group for imperial costuming.
There are units--either garrisons or squads--in various cities, states, regions, countries, etc.
Cloud City Garrison, which covers Oregon and SW Washington, is one of the 501st Garrisons.
Now, within in the 501st, because there's such a variety of costumes, there are speciality groups that focus on specific costumes. These are called detachments. The First Imperial Stormtrooper Division (also called FISD) is the detachment that focuses on TKs. Their website is whitearmor.net. There are detachments for most any other bad guy costume you can think of.
Spend some time exploring the resources and links available from 501st.com. Ask us any questions you have. We'll be able to answer or point you in the right direction.