The study by the non-profit and non-partisan Center for Studying Health System Change in Washington analyzed data from its Community Tracking Study 2003 Household Survey, which included information on 46,600 people.
Safety net providers are those in the public health system who offer care to the poor at reduced or no cost -- and include community health centers.
From interviews done with the uninsured, HSC researchers believe only 18 million -- of 45 million uninsured overall -- know of or use the safety net in their area.
Those that do not know about these healthcare options include 4.6 million uninsured poor and more than 8 million minorities who lack health coverage.
About 8 million uninsured do not know there is a safety net healthcare provider in the community -- despite living within 5 miles of a community health center.
Even though millions of uninsured, low-income Americans are unaware of these services in their communities -- the study found they still are more likely to be aware of them than higher wage earners who do not have health coverage.
2014: The Year in Music [PHOTOS]