The names Highfield and Highfill seem to have been used interchangeably for a period. The marriage record lists her name as Elizabeth Highfill, as does the death certificate for her son Zachary Taylor, but the death record for her son John McCargo and her daughters Hettie and Martha all list it as Highfield. I am using Highfield because it seems to be the variant used by most descendents.

1840 census of Pendleton Co., Ky, lists on p. 234, line 3:
W. Pettit, 1 m 20-29, 1 f < 5, 1 f 20-29.

1850 census of Pendleton Co., Ky, enumerated 13 Aug, lists on p. 16 as family #106:
William A. Pettit, 31, farmer, Elizabeth, 33; Margaret, 10; Sarah E., 8; Zackanah, 3; George T., 10/12.

1860 census of Pendleton Co., Ky, Morgan P.O., enumerated 10 July, lists on p. 128 as family #875/874:
Wm Pettitt, 42, farmer; Elizabeth, 44; Margaret, 21; Sarah, 18; Zackriah, 12; John M., 8; Hetta, 6; Martha M. F., 4; Wm H., 8/12; John M. Smolley, farm worker. All born in Ky.

The next household is that of William Angell, age 76, Wm Pettit’s grandfather and namesake.

1870 census of Pendleton Co., Ky, precinct 7, Collinsville P.O., enumerated 22 June, lists on p. 502 as family #61:
Pettit, Elizabeth, 54; Zack, 23; John, 18; Hettie F., 16; Martha M., 14.