There are some 30+ American states that have tartans, but not all of these are official. That means that not all of them have been adopted by the state.

Of course there are also counties, cities, and towns that have tartans here in America, and even broader regions like mountain ranges (there is a Blue Ridge tartan, for instance).

I have most of these pictured at http://www.district-tartans.com but if you want more information, you really need to buy my Compendium of District Tartans (which you can get to by clicking "Book" on the above web site).

For example, here is the entry from the CDT for the Kentucky tartan (minus the picture):
Kentucky
Date: 2000
Source: Ferguson/Murray-Schweitzer

Kentucky is the “Bluegrass State.” It is home to such American icons as Bluegrass music and the Kentucky Derby.
Kentucky is one of the states that saw a strong Scots-Irish influence as frontiersmen from the southern Appalachians pushed further west. Daniel Boone is but one famous example.
The Kentucky tartan was designed by Rupert Ferguson and Pat Murray-Schweitzer of the Scottish Society of Louisville. Green and blue represent the famous bluegrass of Kentucky. Blue also represents the Ohio and Mississippi Rivers, as well as Lake Barkley and Kentucky Lake, two of the largest man made lakes in the world. Red represents the state bird, the cardinal, as well as the blood shed by Kentuckians defending their nation. White is for the values of purity, goodness, bravery and valor. Yellow is for the state flower, the goldenrod. Black represents coal and oil, two major economic resources in the state.
Kentucky is also the birthplace of both President Lincoln and President Davis, who led opposing sides during the Civil War. This unique fact is honored in the blue and gray in the tartan.
Governor Paul Patton of the Commonwealth of Kentucky signed a proclamation establishing this tartan as the official Kentucky Tartan on April 5, 2000.

K4 G26 B22 W4 N8 R6 Y6
Aye,
Matt