If this is the right Thomas, info from Census records.
Born 1781 in VA120,439 or around 1792 in Upshur County.764
Listed in the 1836 Petition for John McCulloch’s estate.716
Shirley C. Eagan has copies of a promise to pay dated 1855; note where he and Samuel conveyed 40 acres of land in Tyler Co., VA.766

1820 Census, Aleppo Twp., Greene Co., PA, p. 328:
Grim, Thomas
1 male 26-45 (Thomas, 27)
2 females under 10 (Melinda, 3, Lucinda, inf.)
1 female 16-26 (Rachel, 25)

1830 Census, Aleppo Twp., Greene Co., PA, p. 390:
Grim, Thomas
1 male under 5 (Thomas, 1)
2 males 5-10 (James,4, Alfred, 9)
1 male 30-40 (Thomas, 37)
1 female under 5 (Martha J., 4)
1 female 5-10 (Mary, 6)
2 females 10-15 (Lucinda 10, Melinda, 13)
1 female 30-40 (Rachel, 35)

1840 Census, Jackson Twp., Greene Co., PA:
Grim, Thos.
1 male under 5 (Samuel, 4)
2 males 5-10 (Micajah, 7, Armstrong, 8)
1 male 10-15 (Thomas, 11)
2 males 15-20 (James, 14, Alfred, 19)
1 male 20-30 (?)
1 male 40-50 (Thomas, 47)
1 female 10-15 (Martha, 14)
1 female 15-20 (Mary, 16)
2 females 20-30 (Lucinda, 20, Melinda, 23)
1 female 40-50 (Rachel, 45)

1850 Census, Jackson Twp., Greene Co., PA, p. 324, Oct. 9, 1850:
Grim, Thomas, 56, farmer, b. PA
Rachel, 54, b. PA
Thomas, 21, b. PA
Armstrong, 19, b. PA
Micajah, 16, b. PA
Samuel B., 14, b. PA
McCullough, Mary, 15, b. PA

Thomas was living with his son, Samuel, in Tyler Co., WV during the 1870 Census. It gives his birthplace as VA and calculates his birth years as ca 1793, which would agree with the Upshur County date above.767 In 1867 he first applied for a pension due to the service and death of his son, Armstrong during the Civil War. At this time Rachel was still alive. In 1871 when he re-applied he was living with Samuel. On Jan. 13, 1871 Thomas signed a paper, with Daniel McCullough and Samuel V. Grim as witnesses, that his original application was incorrect; in the original he stated his date of marriage was Feb. 13, 1814, but that the actual date was Feb. 13, 1817. He said the mistake probably occurred because he didn’t hear correctly when the papers were read to him. This paper needed to be filed since others had stated the 1817 date in their affidavits.768

Thomas could not write; witness his mark in papers for pension application. Some papers in pension application were witnessed by Samuel V. Grim (son) and Daniel McCollough (brother-in-law?). Others were witnessed by Daniel McCullough and Joseph McCullough, probably his nephews.768

Will:
I Thomas Grim of the County of Tyler State of West Va considering uncertainty of life & the certainty of death & being desirous of disposing of what worldly goods it has pleased Almighty God to bless me with during this life I hereby make this my last will & testament in the following form (to wit) First after my decease & my wife Rachel I desire out of personal effects all my just debts & funeral expenses paid Secondly I give of my real estate forty acres to my son Micajah W. Grim and bounded as follows to wit Beginning at my line corner, corner to Evans survey & with his line S 74 degrees E supposed to 75 poles to a ________ in said line maid January 1866 thence a Southern direction crossing the hill so as to include his house & stable where he now lives to a White Oak on Amos Riggs run. Thence down said run to my original line and from that to the beginning with the several lines and corners thereof and if this does not include the said number of forty acres the balance is to be taken off a _______ of my land lying between the Line of Geo. McCullough & Samuel Riggs Beginning at a White Oak nearest the County road running an equal distance on each line leading to & from said corner so as to make the said compliment of forty acres including the piece before described to have and to hold forever Thirdly The balance of my real estate I give & bequeath to my sons Thomas Grim & Samuel Grim jointly to them and their heirs forever. Fourthly & lastly I hereby appoint my sons Thomas Grim & Samuel Grim my Executors of this my last will & testament In Witness thereof I have hereunto set my hand & affixed seal this 25th day of January 1866.
Signed and sealed in our presents Thomas Grim (His mark)
and by his request signed the
same as witnesses declare the
same to be his last will & testament
Witnesses
A. L. Corbly
Daniel McCullough

Tyler County Court June Term 1873; This Last Will of Thomas Grim late of Tyler County, deceased was this day prosecuted in Court and the execution of said Will by the said Thomas Grim was fully proven by the oaths of Andrew L. Corbly and Daniel McCullough subscribing witnesses to the same and thereupon the said Will was ordered to be recorded as and for the Last Will and Testament of the said Thomas Grim, deceased. And on the motion of Thomas Grim and Samuel Grim, the persons named in said Will as Executors thereof this day approved in Court and made oath as such Executors and together with Canada Vandegrift their security entered into and acknowledged a bond in the penalty of Two Hundred Dollars conditioned as the law directs certificate is therefore given them the said Thomas Grim and Samuel Grim for obtaining probate of said Will in due form of law.
Teste D. Nickman Clerk769