Kiribati celebrates New Year first among inhabited places because its Line Islands use the UTC+14 time zone. The country’s eastern islands lie on the far side of the International Date Line from most of the world.
Kiribati moved the date line around its territory in 1995 so that the nation’s widely separated islands would share the same calendar date. The change made the Line Islands the first locations to enter each new day by civil time.
Kiritimati, also called Christmas Island, is the largest of the Line Islands and is often mentioned in descriptions of the first New Year celebrations. It is not the same island as Australia’s Christmas Island, which is in the Indian Ocean.
The phrase “first country” depends on whether one means an entire sovereign state, an inhabited place, or a particular island. Kiribati is the standard country-level answer, while nearby Pacific states also enter the new year very early.