Botanical gardens, university biology departments, local garden shops and gardening books are all resources that may provide information on native grasses. The Lady Bird Johnson Wildflower Center at the University of Texas at Austin maintains a native plant database of over 7,000 plant species native to North America. Database users can do a basic search of grasses and narrow their search by state.
The USDA maintains a database on their website. The user can type "grass" into the search field and go to a list of grasses. When they select a grass from the list, they are shown a picture of the plant, general information about the plant and a map of where it grows. For example, Mormon needle grass grows in the South-western United States from Texas to California.
Plantnative.org, although geared towards professional gardeners, also provides information on native grasses and provides information on local gardening organizations and recommends books.
Two books by Stevie Daniels, "Easy Lawns: Low-Maintenance Native Grasses for Gardeners Everywhere" and "The Wild Lawn Handbook: Alternatives to the Traditional Front Lawn," provide information on native grasses.
Many scientists consider a plant species native to North America if it grew before European immigrants introduced European varieties, approximately 150-200 years ago.