Needless to say, the southernmost part of the United States is the state of Hawaii. The most north and west are also very good answers, all of Alaska. What many people can’t think of is that the easternmost state is actually Alaska!
Under Alaska, there is a long chain of islands called the Aleutian Islands, and the 180-degree warp passes through the Aleutian Islands. Some islands go to the Eastern Hemisphere, so they become the easternmost territory of the United States.