When you consider the 50 states, the easternmost point is Semisopochnoi Island in Alaska. The westernmost point is Amatignak Island is also in Alaska. (For other extreme points of the USA please check this website :
This confusing fact is due to the presence of the 180th Meridian in Alaska - in the Aleutian Islands area.There are 360 degrees lines in longitude around the world. The Prime Meridan in Greenwich England is the starting point, 0 degrees - ie it is the line where it is the least eastern and western in the world. The 180th Meridan is exactly opposite to the Prime Meridan - the most eastern and western in the world. If you are actually on the line, you are neither east nor west. But step a degree either side, then you would be 179th degree west or 179th east - the highest numbers you can get.