The Federal government was saying we had 7 - 8 million illegal immigrants around 2000, and the Federal estimate gradually increased to 11 - 12 million.
Again, the Feds were wildly inaccurate in the 1980s.
Yale Insights: Yale Study Finds Twice as Many Undocumented Immigrants as Previous Estimates
September 21, 2018"Generally accepted estimates put the population of undocumented immigrants in the United States at approximately 11.3 million. A new study, using mathematical modeling on a range of demographic and immigration operations data, suggests that the actual undocumented immigrant population may be more than 22 million."
"...After running 1,000,000 simulations of the model, the researchers'
95% probability range is 16 million to 29 million, with 22.1 million as the mean."
"...Kaplan and Feinstein have worked on this type of problem for many years. "The analysis we've done can be thought of as estimating the size of a hidden population," Kaplan says. "People who are undocumented immigrants are not walking around with labels on their foreheads. Neither are populations of homeless people, neither are populations of drug users, and neither are populations of terrorists. Yet for policy, it is very important to know the size of these hidden populations because that sets the scale of the problem in each of these different policy areas." "
https://insights.som.yale.edu/insights/yale-study-finds-twice-as-many-undocumented-immigrants-as-previous-estimates 
