The number of people arrested for illegally crossing the southern border from Mexico dropped in October for a fifth consecutive month, down 73% after hitting 132,000 arrests in May.

More than 35,000 people were apprehended by Border Patrol agents for illegally entering Texas, New Mexico, Arizona, and California between official crossing points last month, U.S. Customs and Border Protection officials said Thursday.

The number of arrests in October was down from around 40,000 in September, 50,000 in August, 71,000 in July, and 94,000 in June. CBP uses the number of arrests as an indicator of how many people tried to illegally enter the country, since it is not able to stop every person who tries.

The number of arrests has dropped significantly since Mexico deployed more federal police and military to the U.S. and Guatemalan borders to deter illegal immigration.

In late May, President Trump — frustrated by the lack of legislative action in the U.S. to address the crisis — followed through on a threat to impose tariffs on Mexican imports if the country did not take action to deter people passing through Mexico from Central America on the way to the U.S. southern border.

The Mexican government deployed its National Guard to the U.S. border to prevent people from crossing in well-traveled spots. It also sent the Guard and federal police to its southern border with Guatemala to prevent people from entering into Mexico. Other federal law enforcement and military set up checkpoints along highways in Central Mexico to stop buses of people traveling north. Those without legal documents are arrested and deported.

An additional 9,800 people applied for asylum in October at official crossing points, known by CBP as ports of entry. They did not illegally enter the U.S. and were not arrested.

Acting CBP Commissioner Mark Morgan said at the White House earlier Thursday that the majority of people arrested for coming into the country without permission were adults, not people traveling as a part of a family, marking the first time in more than a year that families were not the majority. He also said Mexican citizens were the most-seen nationality of illegal entrants, not Central Americans.

“We saw a shift — for the first time in nearly 18 months — Mexico was the country of origin for the majority of apprehensions and inadmissible aliens rather than from the Northern Triangle countries, with single adults surpassing families,” Morgan said.

Those taken into custody by Border Patrol are supposed to be held no more than three days in regional stations before being transferred to Immigration and Customs Enforcement. Border Patrol saw an average of 3,500 people in its stations at a time daily in October compared to the nearly 20,000 it had in custody at one point in May, Morgan added.

Arrests of people entering without documentation have slowly ticked up from about 300,000 in 1970 to between an average of 1 million and 1.5 million each year from the mid-1980s through 2006, according to Border Patrol data. October’s total of 35,000 is a rate consistent with 420,000 arrests per year.

[Also read: The illegal immigrant family photos lining the wall of a remote Border Patrol station next to Canada]