Morgan Co., Ky marriage records list the marriage on 3 Aug 1877 of Andrew Brown, age 31, and Mahala Cassity, age 21.

The ages would fit right for Mahala to be the daughter of Thomas Cassity and Elizabeth Brown, who was born on 8 Jan 1856, and whom I have no other marriage data for. But that Elizabeth Brown was (at least according to my database) Andrew’s older sister, which would make Mahala his niece. The other possibility is Mahala Cassity born about 1857, daughter of William H. Cassity (whose wife was also named Elizabeth, maiden name unknown). But she married Newton Cornett in 1894, was still single with her father in the 1880 census, and in the 1900 and 1910 censuses was listed as having no children.

So either there is another Mahala Cassity not listed under that name in the 1860 and 1870 censuses, or I have the wrong parents for Elizabeth Brown who married Thomas Cassity. I believe I got that from various online Cassity trees, and it may be incorrect.

1880 census of Morgan Co., Ky, Blairs Mills precinct, enumerated in June, lists on p. 15 as family #129:
Brown, Andy, 35, farmer; Ann, 22, wife; Eliza, 2, dau; Edith, 45, sister, single; Henry, 16, nephew; Andrew, 9; nephew; Mary, 5, niece. All born Ky Ky Ky.