Yilan County (Chinese: 宜蘭縣; pinyin: Yílán Xiàn; Wade–Giles: I²-lan² Hsien⁴) is a county in northeastern Taiwan. Yilan is officially administered as a county of the Republic of China.

The name Yilan name derives from the aboriginal Kavalan tribe. Other former names in reference to this area in the Yilan Plain include Kabalan,Kavalan, La-A-Lan,E-A-Lan, and Gilan. Before 2009, the county's official name was transliterated as Ilan.

Since early ages, many people have traveled from far places to Yilan. Indigenous tribes that have settled in Yilan are Kavalan people and Atayal people.

The Kavalan people came by the sea and lived by the river at Yilan Plain since around 1,000 years ago. They mostly speak the Austronesian languages. Their settlements consisted of small villages along rivers with around 40-50 communities scattered around the area with a total population of approximately 10,000 people. The Atayal people came by crossing the Xiyuan Pass and settled in the mountain areas.

The Atayal people arrived in Yilan around 250 years ago and settled along the upper Dazhuoshui River. Later, the tribes crossed the Siyuan Pass to reach the valley upstream of the Zhuoshui River. These people are the current residents of Datong Township. Other parts of the Atayal people headed east to enter and settle along the Nan'ao North River and Heping North River. These groups are now settled in Nan-ao Township.

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