William Gillis (c. 1797 – July 18, 1869), sometimes spelled Gilliss, was an American fur trader, real estate developer and pioneer who was one of the original founders of Kansas City, Missouri.

[3] In the early 1830s, Gillis moved to Jackson County, Missouri and continued his trade with Native Americans.

[3] After his death, his $500,000 (~11 million in 2024) was inherited by his niece, Mary Ann, who married Benoist Troost, a Kansas City pioneer and friend of Gillis.

A Missouri Supreme Court case was held by Kahketoqua, a native woman whom Gillis married in 1829, over her getting his inheritance money because of their marriage.

[3] Other Native women he married, such as Wa-Wau-tiqua in 1820, and Poquas in 1824, also sued, but they didn't win any money.