Kiribati is widely recognized as the first country to enter the New Year because Kiritimati uses the UTC+14 time zone.
Kiritimati, also called Christmas Island, is part of the Pacific island nation of Kiribati. Its location in the Line Islands places it on the earliest civil time zone currently used, UTC+14. When midnight arrives there, much of the world is still on the previous calendar date.
Kiribati moved the International Date Line eastward around its islands in 1994, aligning the country's eastern and western island groups on the same calendar day. The change also made the Line Islands among the first inhabited places to see a new date.
“First country” is a shorthand: Kiribati spans multiple islands and time zones, and the exact first inhabited locations can depend on the date and local observance. Kiritimati, rather than every part of Kiribati, is the key location behind the familiar New Year's claim.