Again, I am only asking about States. There are loads of 'possessions' and other terms, such as Puerto Rico, which are not states. There are some really odd suggestions for Southernmost, and as the southernmost US=protected place is the Scott-Amundsen base at the South Pole...
So here are the answers NEWS based entirely on States, and not on territory.
48:
Lake of the Woods, Minnesota
Sail Rock, Maine
Cape Alava, Washington
Rio Grande south of Brownsville, Texas
50:
Point Barrow, Alaska
Peaked Island, off Attu Island, Alaska (past the 180 degree line of longitude)
Ogliuga Island, Alaska (or various rocks not QUITE past the E/W longitude split)
Ka Lae, Hawaii