Newly released government data show 99% of people arrested for attempting to illegally enter the United States in the fiscal 2019 were picked up at the country’s southern border with Mexico.

A total of 859,501 people were taken into custody from Oct. 1, 2018, through this September. Exactly 851,508 people within that figure were arrested for entering the country between official crossing points in California, Arizona, New Mexico, and Texas.

The remaining 8,000 illegal crossing arrests took place along the U.S. border with Canada or in other areas, including Puerto Rico and the Pacific and Atlantic coasts.

The large majority of border arrests have historically occurred at the southern border, though the demographic changed significantly in 2019, according to data from Border Patrol’s parent agency, Customs and Border Protection.

Historically, the majority of people arrested by Border Patrol agents who patrol the fenced and unfenced land between crossing points were Mexican men seeking to get into the U.S. and avoid being caught.

The earliest CBP data available on its website is for fiscal 2007. In that year, of the approximately 876,000 people arrested at any part of the U.S. borders, 808,000 were Mexican citizens, according to its spreadsheet.

Over the last decade, the number of Mexicans being apprehended has drastically declined, while the number of unaccompanied children, families, and individuals from Central American countries has increased.

In 2019, Border Patrol agents took 473,682 family members into custody. One year earlier, only 107,212 people who arrived at the border were part of a family.

A 2015 court ruing in the Flores settlement agreement mandated immigrant children, including those accompanied by a parent, not be held in federal custody more than 20 days. The decision forced Immigration and Customs Enforcement to release massive numbers of people because immigration judges cannot hear new cases for at least two to five years.