The easternmost/westernmost points of the U.S. throughout the world are disputed. What is most eastern or western depends on one's point of view about what east and west really mean.
By cartographical convention, the Prime Meridian running through Greenwich, England is the least eastern and least western place in the world. It is defined as 0 degrees longitude. The 180th Meridian, on the opposite side of the globe represents the absolute limit of how far east or west one can travel, from a cartographical perspective. Anything exactly on the 180th meridian is neither east nor west; but take a single step to either side and one is at 179+ degrees east or 179+ degrees west, the highest achievable numbers. By this mode of reckoning, the most eastern and western spots in the US are both in the Aluetian Islands, Alaska.
If one takes the view that the easternmost place is where the day first begins, and the westernmost is where the day last ends, then the International Date Line is the defining limit for what is most eastern or western. In a new year, the earliest US sunrise takes place on Wake Island. Less than an hour earlier, the sun also rose over Attu Island, Alaska but for December 31.
There is debate on this question but as the above Wikipedia quote shows Alaska would be more appropriately considered more eastern than Maine.