The 1996 Welfare Reform Act (PRWORA) made it more difficult for non-citizens to access means-tested welfare benefits. However, that law also allowed states to use their own funds to extend means-tested welfare benefits to non-citizens and some took advantage of this. After 1996, the only sure-fire way for a non-citizen to get welfare benefits was to naturalize and become a citizen.
Twelve states did not change non-citizen eligibility for four large welfare programs (TANF, SNAP Medicaid, and SSI) in response to PRWORA while the other 39 states and the District of Columbia became more restrictive. If non-citizens responded to welfare reform by naturalizing in order to gain access to benefits then there would be a larger increase in naturalizations in states with more restrictive post-PRWORA policies. The evidence bears this out for immigrants based on country of origin. The state by state evidence is more mixed.
I then compared the increased percent in the number of naturalizations per state from the 1993-1995 period (first period) to the 1997-1999 period (second period). Unfortunately, the 1996 data is unusable because some of it is unavailable and computer problems delayed naturalizations for that year, causing a 100 percent drop off in some states that had nothing to do with welfare reform.