This is the first of what may end up as a series of posts on the statistics of illegal immigration across the Mexican border.
Unlike my usual style, I’m just going to present my conclusions here, and put the citation of sources, evidence, and analysis in separate posts. If I get around to it. Because, to be fair, the conclusions aren’t what I expected to see. And this is a topic where I don’t think people’s opinions are much swayed by evidence anyway.
One simple question: How do they know?
Source: How to Lie With Statistics, 
I didn’t intend to do a series of posts on this topic. I just wanted a simple answer to what I thought was a fairly obvious question. The most basic question you can ask about a statistic, as shown above.
That snowballed. But here’s where I started.
You’ll see various posts and news reporting (loosely defined) claiming that millions of illegal immigrants are coming into the U.S. every year, via the Mexican border.
These claims immediately pinged my bullshit detector, for a very simple reason:
How do they know?
For every law enforcement statistic I know of, official numbers count those who were caught. But here, how do they count the people who weren’t caught, the ones who made it safely (but illegally) into the U.S., via the Mexican border?
Once you start prying away at that question, you soon discover a whole nested set of additional questions. A set of matrioshka cans-of-worms, if you will.
But let’s just stop at the first question.
How do they count the people who successfully illegally immigrate across the U.S.-Mexican border?
The answer, in brief
The answer is, they don’t. There are no hard data or official statistics on that. There are only soft estimates, from various indirect methods.
But the full answer to that question will please nobody.
First, if you see something like “two million illegal immigrants crossed into the United States last year”, that’s a classic intentionally misleading statement. Because that needs to be, but never is, followed with “and were immediately caught and kicked out”.
What I’m getting at is the often-cited 2 million (or 2+ million) figure comes from the U.S. Border Patrol, and is their count of border “encounters” in 2022. Which is their buzz-speak for persons caught and kicked out, and variations on that, including those expelled without legal proceedings during the pandemic emergency.
(You can tell that it’s intentionally misleading because in mainstream news sources, that’s always phrased in a way that’s technically correct. But just barely. Something like “crossed the border” or “crossed into the United States”. Anything that gives the impression that they have become permanent residents of the U.S., without actually stating that this is the count of persons who crossed the border, were immediately caught, and were subsequently expelled.)
That official count, by the way, is a puzzling statistic in its own right, when used for discussions of border security. Are you happier if that goes up, so they catch more people, or if it goes down, so they catch fewer people? With no further context, you just can’t say. You have to make an assumption about enforcement effort and efficacy in order to interpret the direction of any changes. If it goes down because fewer people are trying to enter illegally, that’s a good thing. If it goes down because we’ve slacked off on catching them, or they’ve gotten better at evading security, that’s a bad thing.
Second, some people try to cross that border and don’t get caught. How many do that? There’s no hard data on that, only indirect estimates. These might be derived from survey data — hence the title of this post. Or from calculations that compare U.S. Census estimates of the foreign-born to immigration statistics on naturalized citizens. (The gap between them is presumed to be illegal immigrants living in the U.S.).
What are the odds of successfully making it into the U.S. via Mexico, on any one attempt? Based on those various sources, somewhere around 50/50. It depends on the era, and on the methods, and on whom you are asking. (For example, U.S. Border Patrol says its far less than that, but they are an outlier in that regard). As a good working estimate, somewhere in the 30% to 50% range. (And, of course, people make multiple attempts, so overall likelihood of crossing, for a determined individual, is better than 50/50).
Doing the math, if those multiple indirect methods for counting successful illegal immigration are plausible, and if the current wave of immigrants at the Mexican border is as competent at avoiding capture as prior waves, then the number of people successfully achieving illegal immigration across the Mexican border is arguably somewhere around a million a year, currently.
Give or take a few 100K souls.
You don’t see that number cited because it’s not anybody’s official count, it’s just a a reasonable estimate. From the standpoint of generating click-bait headlines, or riling up the base, that’s not nearly so satisfying as citing the wrong numbers (unsuccessful attempts at illegal immigration), from the U.S. Border Patrol.
Third, it has always been this way, in the sense that the U.S. has never had a secure border with Mexico. At least, not since anyone has tried to keep any comprehensive statistics on border crossings. No Democratic President has had one. No Republican President has had one. For as long as anyone has tried to estimate the “success rate” of a single attempt at illegal border crossing, it has been somewhere in the 30% to 50% range.
And, it has always become an issue during spikes in immigration. And it has always died down as an issue, after those spikes in immigration have passed.
Sources: See last section
Finally, in four+ decades of trying, nothing has worked to reduce that success rate much. Despite the walls, fencing, and technology that has been thrown at the problem — including giving the President carte blanche to disregard virtually all other laws, in setting up barriers at the border (2006 act) — nothing has stopped that. And nothing appears even to slow it down very much.
The numbers go up and down, as shown above. But that’s due almost entirely to fluctuations in the number of people attempting to cross the border. Near as I can tell, the fraction of attempts that are successful hasn’t changed materially — in so far as anybody can tell — in the past half-century or so.
Those last two aren’t my conclusions, drawn out of thin air. Those are the conclusions of the various government agencies and contractors who have studied this problem, in depth, over the past 30 years. As the Congress has passed legislation trying to address the issue.
Anybody who tells you that this is not a problem, or that this is a problem with an obvious solution, is fooling either themselves, or you. Or both.
Details will follow in subsequent posts, if I feel like laying all that out. As I said, this doesn’t seem to be a topic for which facts matter much.
Immediate policy implications?
But if I had to sum it up, so far, if the goal is to reduce the number of illegal immigrants crossing from Mexico, there’s a really good case to be made that the more effective approach is to reduce the number of people who want to enter the U.S., than it is to layer on more of the existing types of border security. Because, at least so far, all the walls and fences and technology that have been thrown at this issue haven’t done much to increase the odds of getting caught. Once the would-be border crossers get used to the new setup.
This doesn’t even address the fact that prior to the last few years, the Mexican border wasn’t even the principal source of illegal immigrants in the U.S. Again, in so far as anyone could tell. That population consisted mostly of people who overstated their legal visas. They entered legally, but stayed illegally.
Maybe you could argue that we just haven’t done enough, in terms of traditional border security. But that’s a relatively tough argument to make, given that about a third of the entire length of the border already has fences or walls (about 700 miles of the roughly 2000-mile border), reflecting mostly the 2006 legislation shown on the graph above. And a police force of about 20,000 persons (officers of the U.S. Border Patrol) already patrols that border. Along with sensors and satellites and drones and such.
And then there’s the history. Just about once a decade, some U.S. President Does Something about this issue. Surges in border-security spending, in response to surges in immigration across the Mexican border, go back at least to Reagan. And yet, here we are, again. So it’s really an act of faith to say that this round of throwing more money at the problem will succeed.
I suppose we could set up a Soviet-style East Germany/West Germany border, complete with a no-man’s-land kill zone and machine gun emplacements every 100 yards. At that point, until you ran out of money or ammunition, you would probably succeed in keeping people from crossing that border. And, based on the rhetoric, I’m sure that there are Americans who think that would be a dandy way to keep immigrants from “tainting the blood” of America.
Weird factoid: That whole focus on “blood” has a long history in literal U.S. legal immigration policy. Turns out, we used to set immigration quotas by country, for many countries, and the quotas were explicitly calculated to keep the “blood mix” of the U.S. population constant. That is, if x% of the population at the time of quota enactment was of Italian ancestry, then x% of the total legal immigration quota was allocated to Italians. That way, individuals of Italian ancestry would neither increase nor decrease as a fraction of the population, due to immigration. Funny, but I never learned that in school when we were learning about America being the great melting pot of the world.
But I don’t think that’s a majority view. Or, at least, I hope that wouldn’t be. A focus on extreme security measures of that nature suffers from the same drawback as (e.g.) stripping children away from their parents and intentionally turning them into orphans. All moral issues aside, gunning down families attempting to cross the border would make us look bad.
But I can’t deny that it would probably be effective in deterring people from trying to enter the country across that border.
In this context — that the Mexican border is like a sieve, and there doesn’t appear to be much we can do about it, violent fantasies aside — then the current Administration’s focus on trying to resolve the basic issues that are driving people out of Central and South American countries makes some sense. The fewer people who are pushed out of their birth countries, the fewer will end up on our border. Whether that’s more effective, or less effective, dollar-for-dollar, than beefing up traditional border security, is certainly questionable.
Right now, the Biden administration is busy using existing funding to patch the worst known holes in the border (reference). For some reason, Biden got a lot of grief for doing this, but a) the Congress passed the legislation requiring additional construction, and b) the 2006 legislation that authorized the first 700 miles of fence gave the sitting President the right to waive any and all other laws, including environmental laws, when putting up a border fence with Mexico. He’s just executing the will of the Congress, as expressed in law. (Look up the the Congressional Budget and Impoundment Control Act of 1974, if your thinking on this issue remains mired in powers that Presidents used to have.)
I suspect that any legislation this year (we’re about due for it, per the graph above) will do pretty much the same. Slap on a few more patches, and just keep going.
Did apprehensions peak in 2022?
Source: These are data by fiscal year, including apprehensions at the border, and Title 42 COVID “expulsions” (when applicable), but do not include “inadmissables” denied entry when presenting themselves for entry to the U.S. at border stations. Data through FY 2018 are from U.S. Border Patrol, United States Border Patrol, Southwest Border Sectors, Total Illegal Alien Apprehensions By Fiscal Year. Data for later years are summarized from downloadable files from the U.S. Border Patrol, “sbo_encounters”, summarized by fiscal year, including only COVID (Title 42) and apprehensions, to be consistent with the earlier data. A typical data source can be found on this USBP web page. Beyond this time period, for the first three months of FY 2024, encounters are down by about 8% compared to last year (from this reference).
Short answer appears to be yes. But not by much. Unless this peak in immigration is unlike prior peaks, then peak attempts at illegal immigration across the Mexican border occurred in FY 2022, with 2.2 million apprehensions of various sorts. That fell to about 2 million in FY 2023. And that continues to fall slightly in FY 2024.
There’s some ambiguity in the peak because these are counts of the number of times persons were apprehended and removed, including removals under Title 42, the public health emergency for COVID. That allowed expulsion of individuals from selected countries with no legal processes whatsoever. But those COVID-based removals came with a catch. They avoided the legal processes normally required for deporting individuals. But because of that, you can’t say that the folks removed that way were convicted of a crime. So, for those removed that way, there was no additional penalty for trying again. As opposed to those who had been legally deported on other grounds. And so, apparently, a lot of them did, and the rate of recidivism (people caught several times, attempting to cross the border) increased during that period. Those removals ceased with the end of the COVID-19 public health emergency last year. But even if you made a reasonable attempt to net out the higher recidivism rate, I’m pretty sure 2022 stands as the new peak.
Based on past behavior, the Congress will act just past the peak of the most recent wave of immigration. So we’re just about due to have another immigration reform bill passed.
But there are some odd things going on this time around. In part, there’s presumably some catch-up from COVID. But there’s also been a profound shift in the mix of countries of origin. Historically, almost all apprehensions at the border were Mexicans. Now, Mexicans are the minority, and most of what’s showing up is from countries south of there, many with current political and economic crises. (But when in the past few decades has there not been political and economic turmoil in Central and South America?)
At any rate, what you see above is a consistent time series on folks caught trying to enter the U.S. illegally at the Mexican border, and expelled, one way or the other.
You’ll have to make up your own numbers on the count of those who succeeded in crossing the border illegally. Until such time as we can ask them all to raise their hands and be counted.
