I can't vouch for how the data are collected, but this Bing shows a lot of reports that say there are more Visa overstays. 
https://www.bing.com/search?FORM=SLBRDF&pc=SL15&q=Visa%20Overstays%20vs%20Illegal%20border%20crossing
Oh, I understand that, and it is an issue that needs to be addressed. As I said, there's no excuse for this being ignored by the people who issue the visas and should be responsible for enforcing their use.
But - as we know, the feds are very, very reluctant to produce actual illegal immigration numbers and in fact, go to great lengths to obfuscate the issue.
From one of those articles in Bing: "Of the
482,781 aliens who were recorded to have overstayed temporary U.S. visas in fiscal year 2015, just 2,456 were successfully deported from the United States during the same period, according to DHS’s figures, which amounts to a deportation rate of around 0.5 percent."
Looking at illegal border crossing types, the numbers are all over the place. If you see "11 million" it is usually attached to a federal and/or left-wing type article, but even those show the 11 million at wildly varying points in time. Did we get to 11 million in 1990 or 2015?
According to Wikipedia: "The number of illegal immigrants peaked at about 12 million in 2007 and since that time has declined.[1] According to the nonpartisan Pew Research Center, the estimated population of illegal immigrants in the U.S. rose rapidly in the 1990s, "from an estimated 3.5 million in 1990 to a peak of 12.2 million in 2007," then dropped sharply during the Great Recession before stabilizing in 2009.[2] Pew estimated the total population to be 11.1 million in 2014, or approximately 3 percent of the U.S. population.[3][2][4] This "is in the same ballpark" as figures from the United States Department of Homeland Security (DHS), which estimated that 11.4 million illegal immigrants lived in the United States in January 2012.[1][5] The estimate and trends are also consistent with figures reported by the Center for Migration Studies, which reported that the U.S. illegal immigrant population fell to 10.9 million by January 2016, the lowest number since 2003.[6]"
Now, keep in mind that 0bama "legalized" a large number of this population, which may account for much of the so-called decrease.
Fairus.org estimates 12.5 million.
https://www.fairus.org/issue/illegal-immigration/how-many-illegal-immigrants-are-in-usI base my suspicion that the number is much higher on two things: first is purely anecdotal. I see the increase all around me.
The second is the numbers of illegal apprehensions along the SW border for the last four years, which is an average of 380,873/year, and estimates are as high as the Border Patrol apprehending at least 1 of 10 illegal crossers, which would mean actual numbers of 3.8 million entering per year. You can't have 3.8 million per year coming in with no increase or even a decrease in the number of illegals here.
In fact, just being charitable, let's say that the 11 million number did occur in 2014 and not 20 or 30 years ago, when the number started being used. That immediately puts us at +15 million today, not counting deportations.
According to Politifact, we have deported a total of 1.2 million from 2015 through 2017*. That leaves us with over 14 million in just this four year period, but this has been going on since the 80's at least. 11 million is a bogus number.
* This number includes the number of visa overstays who were deported, which further increases the estimated number of illegal aliens currently residing here.
