The early Reagans loved Tennessee
The majority of Reagans who came to Texas in the early 1800s were from Tennessee, Sevier County, to be exact. And a bunch of their ancestors settled in Tennessee from Maryland after emigrating from Ireland. That may be the case with my Reagan branch.
The Timothy Reagan (or Ragan) who was born in Maryland in 1678 (died in 1744) may be my 6G-grandfather. He had a son named Reason (Rezin) Reagan (1720-1763) who had a son named Thomas (5/6/1749-7/25/1838) who had a son named Rezin. That Rezin married a Leannah Hood. If they had a son named James (1820-1870) who in turn had a son named James as well (born 1857) then it all adds up (See Rezin Clue) and I've all of a sudden found four more generations of Reagan relatives.
Donald B. Reagan of Tennessee has created a wealth of information about the Ragan/Reagan family of Tennessee. He has written a book, "The Book of Ragan/Reagan", 1993. You can find his genealogy work at http://www.smokykin.com/