Puerto Rico is closing 184 public schools in a bid to save money amid a deep economic crisis that has sparked an exodus to the US mainland in the past decade.
Education Department spokeswoman Yolanda Rosaly said officials will relocate 27,000 students to other schools.
The closures will occur once the school year ends this month.
The island has a total of 1,292 public schools that serve 365,000 students.
Ms Rosaly said Education Secretary Julia Keleher would provide more details soon.
Puerto Rico has seen school enrolment drop 42% in the past three decades and an additional 22% drop is expected in future years.
Nearly half a million people have moved to the US in the past decade.
It is the largest mass closure of schools announced in the history of the US territory. Officials closed 150 schools over the span of five years from 2010 to 2015.
Opponents of previous school closures say that transportation logistics and special education needs were not taken into account.
An estimated 30% of Puerto Rico students receive specialised education, twice the average in the US mainland.
Much of the population drop is the result of parents moving to the mainland US in search of jobs and a more affordable life, as well as thousands of teachers being recruited from the island for their bilingual skills.
The island's low birth rate also is expected to keep driving down enrolment.