According to a recent government report, in the first 6 months of 2014:

• 17.8% of people (47.7 million) under age 65 were in families having trouble paying medical bills, down from 21.3% (56.5 million) in 2011
• Among people under age 65, 31.2% of the uninsured, 24.2% of those with public health coverage, and 12.4% of those with private health coverage were in families who had trouble paying medical bills in the past 12 months
• Families who had trouble paying medical bills in the past 12 months included 27.1% of poor, 28.0% of near poor, and 12.6% of not poor people under age 65

Source: "Problems Paying Medical Bills Among Persons Under Age 65: Early Release of Estimates From the National Health Interview Survey, 2011–June 2014," National Health Interview Survey Early Release Program/National Center for Health Statistics, February 2015, http://www.cdc.gov/nchs/data/nhis/earlyrelease/probs_paying_medical_bills_jan_2011_jun_2014.pdf