Nearly 35,000 individuals were arrested crossing the southern US border illegally last month, according to a source familiar with the latest arrest figures.
In June, 34,911 people were arrested -- down from 40,334 the previous month.
After seeing higher levels of illegal crossings this spring, the administration likely welcomed the news.
But though the Trump administration has made cracking down on illegal immigration a priority, including a policy that had at one point resulted in separating undocumented families, it is nearly impossible to attribute the decline to any specific policy.
Aside from last year, which defied most seasonal border crossing trends, there has consistently been a decline in crossings from May to June dating back to 2000. The size of the dip varies by year.
The administration rolled out a "zero tolerance" prosecution policy at the border in May that resulted in thousands of children being separated from their parents in detention. The practice drew bipartisan condemnation, resulting in Trump reversing course in late June and ordering that families be held together.
Despite an internal prediction that the policy would have a deterrent effect within two to three weeks, apprehensions increased in May, according to documents obtained by CNN.
And although there was a decrease in crossings in June, the figure is fairly consistent with recent months and lines up with numbers from the past several years.
The number of people turned away at legal ports of entry on the border last month is not yet available.
A Department of Homeland Security spokesman said the agency doesn't comment on unofficial numbers.