Hello familysleuth,
Have you anything else about Thomas Jarvis which confirms his year of birth as c1789? Is he shown on census returns, or does his marriage and/or burial support a date of birth c1789?
There is a search facility on the Somerset OPC site:
http://wsom-opc.org.uk/The baptisms on Freereg show that a John and Elizabeth Jarvis/Jarves baptised children in Doulting in 1776 to 1787. Doulting is close to Shepton Mallet, about 3-4 miles at the most.
21/07/1776, John, son of John and Sarah Jarvis.
26/02/1778, Elizabeth, daughter of John and Sarah Jarvis.
10/10/1779, David, son of John and Sarah Jarvis.
08/02/1781, Sarah, daughter of John and Sarah Jarvis.
29/02/1784 William, son of John and Sarah JARVES.
14/01/1787 Martha, daughter of John and Elizabeth Jarves
There is a burial of Martha Jarvis in Shepton Mallet on 26/05/1787. She is shown as aged 6 months.
Another burial in Shepton Mallet for Betty Jervis in 28/05/1788. She is shown as aged 10.
These tend to link the baptisms in Doulting with the family in Shepton Mallet.
There is a marriage of John Jarvis to Sarah Pierce in Binegar in 01/01/1770. Both shown as OTP and By Banns.
Did Sarah die and John remarry? No trace of a burial for Sarah, or subsequent remarriage unfortunately.
It doesn't help you find Thomas Jarvis but may give some clues as to his family line.
Jo.