Krabi’s populace represent a multi ethnic multi racial society. It is a mix, mélange or mosaic of various ethnic groups. Each ethnic group in Krabi represents a page in the annals of immigrants to the area from time immemorial.
Krabi is not over populated just as Thailand in general is. As the country is poised in the middle of the states in the area, plenty of migrations have taken place in the past centuries overlooking geographical boundaries.
In the late 19th and 20th century, people from Chinese mainland, especially the southern area entered Thailand. Even though they came in for supplementing the local labor, they got assimilated into the society. You can see a cross section of the Chinese society in Krabi as well. Chinese rituals and cultural aspects were absorbed in parts by the Thai society as well.
There is an ethnic group called Sea Gypsies or Chao Ley whose origins are not known. But they have been natives in Krabi for quite some time now. They have been a nomadic tribe depending mainly on fishing, collecting shells and diving for sustenance.
75% of the total populace is of Thai origin, 14% are Chinese and the remaining 11% includes all other ethnic minorities including Indians.
Information : http://www.krabi.com/culture.htm

So followers many emigrated in the steps of the Phra Palad that soon Krabi had a large community in three different boroughs : Pakasai, Khlong Pon, and Pak Lao. In 1872, King Chulalongkorn graciously elevated these to town status, called Krabi, a word that preserves in its meaning the monkey symbolism of the old standard. The town's first governor was Luang Thep Sena, though it continued a while as a dependency of Nakhon Si Thammarat. This was changed in 1875, when Krabi was raised to a fourth-level town in the old system of Thai government. Administrators then reported directly to the central government in Bangkok, and Krabi's history as a unique entity separated from the other provinces, had begun.
mainland.The provincial administration also covers more than 130 islands in the Andaman Sea. Natural forest cover is chiefly mangrove and Cassia trees. Krabi's sandy clay soil conditions are perfect for a variety of agricultural products, including rubber trees, palms, mangos, coconuts, and coffee. The Krabi River flows 5 kilometers through the city and falls into the Andaman at Tambon Pak Nam. There are other streams as well : the Khlong Pakasai, the Khlong Krabi Yai and the Khlong Krabi Noi in the province's highest range of mountains, the Khao Phanom Bencha.