Humacao (Spanish pronunciation: [umaˈka.o]) is a municipality in Puerto Rico located in the eastern coast of the island, north of Yabucoa; south of Naguabo; east of Las Piedras; and west of Vieques Passage. Humacao is spread over 10 wards and Humacao Pueblo (the downtown area and the administrative center of the city). It is part of the San Juan-Caguas-Guaynabo Metropolitan Statistical Area.
The region of what is now Humacao belonged to the Taíno region of Jumaca, which covered a portion of the southeast coast of Puerto Rico. The region was led by cacique Jumacao (also referred to as "Macao"). The Taíno settlement was located on the shores of what is called now the Humacao River. It is believed that the Taíno chief Jumacao was the first "cacique" to learn to read and write in Spanish, since he wrote a letter to the King of Spain Charles I complaining about how the Governor of the island wasn't complying with their peace agreement. In the letter, Jumacao argued that their people were virtually prisoners of Spain. It is said that King Charles was so moved by the letter that he ordered the Governor to obey the terms of the treaty.
During the early 16th Century, the region was populated by cattle ranchers. However, since most of them officially resided in San Juan, a settlement was never officially organized.