Before the Han Chinese Wu Sha led his company into large-scale reclamation in today’s Yilan in 1787, the area was mainly inhabited by the indigenous Kavalan people.

During the Japanese rule, much of the present day Yilan County was part of Japan within its Taihoku Prefecture.

Other former names in reference to this area in the Yilan Plain include Kabalan,[3] Kavalan, Kavaland, kap-a-lan, Yiland and Gilan.

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.

Around 200 years ago, at the end of the 18th century, the Han Chinese traversed the mountain range and settled in Yilan.

Large populations began taming the wilderness, cultivating the fields and building irrigation channels.

They then torched harbors and surrounding villages, and even went as far as taking over Su'ao Town and established a city called Saint Lorenzo.

In 1640, the Dutch began contacting Han Chinese merchants for trade and levying taxes on various commercial goods.

During the Kingdom of Tungning era, the previous economy monopoly system developed during the Dutch Formosa continued to be practiced.

The Qing dynasty government subsequently realized that if they continued to disregard the Kavalan people and did not establish rule of law and a system of defense, Yilan would become a haven for criminals and outlaws, a thorn in the side for Taiwan.

[5] After the Mudan Incident in 1874, Qing rulers changed their passive attitude and took a more ambitious approach in ruling Taiwan.

After the First Sino-Japanese War in 1894, the Qing government handed over Taiwan to Japan in accordance with the Treaty of Shimonoseki.

On the three vertices of the triangle sit the Toucheng, Sanxing and Su-ao Townships with a roughly equal distance of 30 km on the three sides.

Large amount of silt carried by the river have little time to settle because of the high slope of the lands where it flows out of the mountains and valleys.

Large amount of gravel accumulate in the shallow stream bed, creating alluvial fans that often forms into web-like pattern.

Train stations within the two lines in the county are Shicheng, Dali, Daxi, Guishan, Wai-ao, Toucheng, Dingpu, Jiaoxi, Sicheng, Yilan, Erjie, Zhongli, Luodong, Dongshan, Xinma, Su'aoxin, Su'ao, Yongle, Dong-ao, Wuta and Hanben Station.