Trump said, "The annual cost of free tax credits alone paid to illegal immigrants quadrupled to $4.2 billion in 2011."
Based on an audit by the Treasury Inspector General, the claim leaves out some context. Trump conflates "illegal immigrants" with "unauthorized workers," a group composed largely of undocumented immigrants but also legal immigrants and others. The $4.2 billion refers to the amount given in tax credit refunds for children, the large majority of whom are U.S. citizens. And the actual year is 2009, not 2011 (that was the year the report was published).
Also, it's important to note that illegal immigrants pay an estimated
$12 billion in payroll taxes to Social Security and don't receive benefits. So Trump is leaving out a significant part of the picture when it comes to taxes and undocumented workers.