叶凯士天文台（Yerkes Observatory）座落于美国威斯康辛州威廉斯湾，附属在芝加哥大学，于1897年由乔治·海尔创立，并获当时大企业家查尔斯·耶基斯（Charles T. Yerkes）资助。

叶凯士天文台拥有一台口径40英吋的折射望远镜，由光学大师克拉克（Alvan Clark）建造，与天文台一起落成启用。这台望远镜直到今天一直是世界上口径最大的折射望远镜。此外天文台还拥有两台40英吋和24英吋口径的反射望远镜。

叶凯士天文台的研究课题包括星际物质、球状星团的形成、红外线天文学和近地天体。该处同时存在一个大小相当的工程中心，专门研制和修理科学仪器。

Yerkes Observatory is an astronomical observatory in Williams Bay, Wisconsin operated by the University of Chicago Department of Astronomy and Astrophysics. The observatory, which calls itself "the birthplace of modern astrophysics," was founded in 1897 by astronomer George Ellery Hale and financed by businessman Charles T. Yerkes. It represented a shift in the thinking about observatories, from their being mere housing for telescopes and observers, to the modern concept of observation equipment integrated with laboratory space for physics and chemistry.