A new study by the Center for Migration Studies estimates that 10.9 million immigrants are living in the country without authorization. That is the lowest level since 2003 and the first time the number has dipped below 11 million since 2004.
The estimates are borne out by empirical observation; increasing numbers of overgrown yards being one variable.
Reportedly, Mexicans have been going back home in large numbers over the past few years, as numerous unfinished structural framing jobs attest. It's alleged that the population of illegal aliens from Mexico has dropped by 9% over the past five years.
Although the study found declines in the number of such immigrants from South America, the Caribbean and Europe, it reported an increase in the number of immigrants crossing illegally from Central America, which has been gripped with rising violence in recent years.
Factors attributed to the return of Mexicans to their country include the decline of the American economy in recent years and less competition for jobs back home. That translates into less incentive to head north, ostensibly.
It should be noted that the Center for Migration Studies generally advocates for "rights" for illegal aliens, so their conclusions are not without bias.