But he appears to be referring to old border fencing built decades ago. And, despite his hard-line policies and tough rhetoric, border arrests have actually spiked in the past year.
Here's a look at what Trump said during a tense meeting with congressional Democrats and why it doesn't match reality:
Trump: "A lot of the wall is built. It has been very effective. I asked for a couple of notes on that. If you look at San Diego, illegal traffic dropped 92 percent once the wall was up. El Paso, illegal traffic dropped 72 percent then ultimately 95 percent once the wall was up. In Tucson, Arizona, illegal traffic dropped 92 percent. Yuma, it dropped illegal traffic 95 to 96 percent. When I say dropped, the only reason we have any percentage where people got through is because they walk and go around areas that are not built. It dropped virtually 100 percent in the areas where the wall is. It is very effective."
Let's break it down claim-by-claim:
New sections of the border wall
Trump: “A lot of the wall is built. It has been very effective.”
Under Trump, the military has installed 70 miles of concertina wire. Separately, border authorities have worked on improving existing structures. Only one of those projects, the Calexico border effort in California, started and finished under Trump.
Also, while Trump says that border fencing has been "very effective," he doesn't mention that illegal border crossings are actually back on the rise.
According to U.S. Customs and Border Protection officials, there were nearly 397,000 people arrested trying to illegally cross the U.S.-Mexico border in the 2018 budget year. That number represents a spike from the 300,000 figure in 2017 and puts levels on par with 2016 before Trump took office.
Trump: “San Diego, illegal traffic dropped 92 percent once the wall was up.”
According to DHS, the “wall” in San Diego was built in 1992, and, the agency spokesperson told ABC News, “Illegal traffic has dropped 92 percent over the past 23 years.”
There has also been a new border construction project at Calexico in California. That 2.25 mile project replaced existing fencing and sits about 120 miles from San Diego. Planning to improve border security there began before Trump took office, but the construction started and finished under his watch.
Trump: “El Paso, illegal traffic dropped 72 percent then ultimately 95 percent once the wall was up.”
DHS tells ABC News, El Paso border security was built in 1993 and afterward illegal traffic “dropped 72 percent in one year and 95 percent over 22 years.”
This administration completed a remodeling project there too, but that project started before Trump was in office.
Trump: “In Tucson, Arizona, illegal traffic dropped 92 percent. Yuma, it dropped illegal traffic 95 percent to 96 percent.”
DHS officials said that the Tucson structure was built in 2000 and Yuma construction started in 2005 -- both well before Trump was elected. DHS officials said that illegal traffic has dropped in Tucson by 90 percent in the past 15 years, and by 95 percent in nine years. This suggests the drop wasn't the result of any of Trump's policies.
Trump: "People are pouring into our country, including terrorists. We have terrorists. But we caught 10 terrorists. These are over the last very short period of time -- 10."
This figure probably comes from Trump's Homeland Security Secretary Kirstjen Nielsen, who has said previously that DHS blocks "10 known or suspected terrorists a day from traveling to or attempting to enter the U.S."
But that figure is not specific to migration at the U.S.-Mexico border.
The State Department said in a report last year that there was "no credible information" that any member of a terrorist group traveled through Mexico to enter the U.S.
ABC News' Anne Flaherty contributed to this report.