Marriage of Thomas Pettit & Behethelon Owen on 16 Apr 1785 is listed in the IGI in three submissions: batch 7013802, p. 97, batch 7732027, p. 68, and batch 8330802, p. 84. They all have the same date and county, but Thomas' name is spelled twice as Pettit and once as Pettet, and his bride's name is spelled variously as Bethethelon Owens, Behethelon Owens, and Bethelon Owen. The second submission is the same one that lists all the Washington Co. Ky marriages of the children listed in the 1834 will of Thomas of that county, which is how I conclude that these are the same individual. Note that the first submission is the same one that listed the marriage of Nathaniel Pettet and Rebecca Owen. (This submission also includes a marriage of Samuel Pettit and Elizabeth Bragg on 10 Dec 1783 in Fauquier Co., VA.)

Will of Thomas Pettit, recorded 7 Sep 1834 in Washington Co., Ky, lists daughters Lucy, Harriet, Jane, and Sally, and son William H. This will is indexed in the IGI, batch 7811106, p.45. (I cannot find a William H. in the 1830 or 1840 censuses of Ky.)

Another possible daughter is Elisa Petet m. William Humphrey, 21 Dec 1825, Washington Co., Ky.

1820 census of Washington Co., Ky, p 18A, lists:
Thomas Petitt (from index only, haven't looked at this yet) (This is the only Pettit in Washington Co. in 1820. There are none in 1830, so Thomas was probably living with the family of one of his married daughters, considering that he was still in the county at his death in 1834.)