Peter Headrick of Murray County must be of a different line. There are four very early records for a Peter Headrick in Murray County, Georgia. There is no evidence to show if how these individuals are related and which records, if any, apply to the same Peter Headrick.
1) Peter Hedrick, resides near John Hedrick [1840 U.S. Census, Murray County, Georgia, p.8. Just a few years prior to that census, the land in Murray County was still part of the Cherokee Nation.]
2) Peter Headrick married Susan Sutton on 19 April 1840 in Murray County, Georgia. (Murray County Marriage Book I, covering 1835-1905, p.58)
3) Peter Hedrick (resident of Lumpkin County, Georgia) bought land lot 282 in the 8th District, 3rd section of Murray County, Georgia, on 26 September 1840 (conditional sale, upon his payment of a promissory note by 25 Dec. 1841). [Murray Co., Georgia Deed Record book G, p.455] I don't know if this Peter Hedrick/Headrick ever lived in Murray County, or if he just owned land there.
4) Peter Headrick married Mary Ann Smith on 13 Feb 1845 in Murray County, Georgia. (I don't have a reference on that fact, so if researching that line, please doublecheck.)
I have nothing to show if any of these records relate to one individual or three different Peter Headricks. If your Pete Headrick married "Pheby," it would appear to be a different Pete Headrick unless she had another name ~ but it is great to have his wife's name. It helps me distinguish the different Pete Headricks. Thanks!
I did take an interest in your Thomas Benton Headrick. I was researching Jacob Headrick and Harriet Hall, of my line. They resided in Murray County, Georgia, and also Polk County, Tennessee. Their son, William H. Headrick, moved to Cullman County, Alabama. He resided there in 1905 and 1910 according to his address on a pension deposition. I've never found him in Alabama census and can't find a death date or location for him. I don't know if other Headricks moved there with him. I found Thomas Benton Headrick in Blount County, Alabama, when I was searching for clues to Jacob and Harriet's son. I wanted to see if Thomas was of any relation to these Headricks. I don't have anything to link them, so far. I can't figure out where your Pete fits in. He's of the age to be a brother to Pete "Dutch" Headrick of Alabama, but researchers have connected that Pete to parents Peter and Rebecca Stephens Headrick, not Pheby. Never rule anything out, though. There are always lineage errors, subsequent marriages, or illegitimacies to consider. Anything like that can throw a wrench into the "facts" that have been published about Headricks.