Kiribati is the island nation commonly identified as celebrating New Year's Eve first among inhabited places because of its time-zone position near the International Date Line.
Kiribati's Line Islands use UTC+14, the world's most advanced civil time zone. Kiritimati, also called Christmas Island, is part of that island group and is frequently highlighted in global New Year reports as one of the first inhabited places to reach January 1.
The situation is the result of a time-zone decision made by Kiribati in 1994. The country moved its eastern islands to the same calendar day as its western islands, eliminating a date difference within the nation. The International Date Line is an agreed convention, not a perfectly straight physical line.
“First” depends on the comparison being made and on whether an inhabited location or a national capital is meant. Tonga and Samoa also celebrate very early, but Kiribati's UTC+14 Line Islands are the usual answer to this specific geographic question.