CBO Paper: The Impact of Unauthorized Immigrants on the Budgets of State and Local Governments [open pdf - 318KB]
"Over the past two decades, most efforts to estimate the fiscal impact of immigration in the United States have concluded that, in aggregate and over the long term, tax revenues of all types generated by immigrants--both legal and unauthorized--exceed the cost of the services they use.1, 2 Generally, such estimates include revenues and spending at the federal, state, and local levels.3 However, many estimates also show that the cost of providing public services to unauthorized immigrants at the state and local levels exceeds what that population pays in state and local taxes. It is important to note, though, that currently available estimates have significant limitations; therefore, using them to determine an aggregate effect across all states would be difficult and prone to considerable error. The impact of unauthorized immigrants on the federal budget differs from that population's effect on state and local budgets primarily because of the types of services provided at each level of government and the rules governing those programs. For instance, most unauthorized immigrants are prohibited from receiving many of the benefits that the federal government provides through Social Security and such need-based programs as Food Stamps, Medicaid (other than emergency services), and Temporary Assistance for Needy Families. At the same time, the federal government requires that state and local governments provide certain services to individuals, regardless of their immigration status or ability to pay, in order for those states or localities to participate in some of its assistance programs."
Congressional Budget Office: http://www.cbo.gov