According to a recent government report, here is a breakdown ...

... of the expected source of payment for emergency department visits made by U.S. adults aged 18 to 64 in 2012:

• 33% - private insurance
• 21% - Medicaid
• 20% - no insurance
• 9% - Medicare
• 5% - worker's compensation
• 11% - unknown/blank

Source: "Expected Source of Payment at Emergency Department Visits for Adults Aged 18–64 for the United States and in the Five Most Populous States, 2012," National Center for Health Statistics/Centers for Disease Control and Prevention, NCHS Data Brief No. 253, June 2016, http://www.cdc.gov/nchs/products/databriefs/db253.htm