Settlement of southeast Tennessee was varied and complex. The earliest settlements in the region was at Jonesboro, TN. first known as the Watauga Settlements. This occurred in the mid to late 1770's. The earliest tax lists for the region are housed in Greene County, TN. Earliest dates are 1778.
Tennessee became a state June 1st, 1796 http://www.50states.com/statehood.htm Prior to that the largest part of the region was held by the state of North Carolina. This particular area was Washington District, North Carolina but also known as Washington County, NC. For an excellent, animated map that shows the progressive county formation in Tennessee please visit www.tngenweb.org
The most prominent factor contributing to the ever-changing county lines were the continual Cherokee and Chickasaw Imdian treaties. A list of these, for the most part but not all, can be seen at www.tngenweb.org and www.accessgenealogy.com
There were no Revolutionary War Land Grants in Tennessee, 'officially'. The lands that lay in Tennessee were in North Carolina at the time of the grants. You'll need to look for "North Carolina Land Grants in Tennessee". An index is online at www.rootsweb.com/~tnmonroe The War of 1812 did see the first grant land laid out in this state.
The Hiwassee Purchase formed the counties of McMinn and Monroe. The settlement of these two counties saw a huge influx of settlers. Most were residents of the Watauga area but some were also from North Carolina, South Carolina and a few from Georgia. The Hiwassee Purchase map shows the first time in this country that a grid system was used. This same system was later used for the Ocoee Purchase that formed Polk, Bradley, Hamilton and James. Each 36 sq. mi. township or fractional township was laid out in sections of 1 sq. mi. Each square mile was then laid out in sections of 320 acres, 160 acres, 80 acres or 40 acres. Specific sections were held for the miltary service grants and some land remained in the hands of Cherokee Indians who'd received 640 acre land Reservations between 1817 & 1820.
The entire situation was much more complex than reflected in these few lines. One of the best pieces of advice to be offered is to 'forget about county lines'. Always, always look into surrounding counties. There is one small section of land in east Tennessee that has been in 4 counties.