This report from the Kaiser Family Foundation analyzes the total enrollment in Medicaid as of December 2009.  

From the report:

Medicaid enrollment rose by 3.78 million between December 2008 and December 2009, the program’s largest absolute 12-month enrollment increase since the early days of implementation in the late 1960s (Figure 1). Medicaid enrollment has risen by nearly 6 million (13.6%) since the start of the recession in December 2007. Between that month and December 2009, the nation’s unemployment rate doubled from 5.0% to 10%. As many Americans lost jobs, incomes, and access to affordable employer coverage, Medicaid enrollment rose to 48.57 million in December 2009. Millions more who did not qualify under their state’s existing Medicaid eligibility criteria likely joined the ranks of America’s now 50 million uninsured.

Full Report: Medicaid Enrollment: December 2009 Data Snapshot (PDF | 992 KB)   

The Kaiser Family Foundation. (2010). Medicaid enrollment: December 2009 data snapshot.