Middlefork Savanna is a 687-acre preserve in Lake Forest, Illinois, where the middle fork of the North Branch of the Chicago River runs through a diverse landscape of oak savannas, prairies, marshes, deciduous woodlands, and sedge meadows. Its most notable feature is 25 acres identified as the highest-quality tallgrass savanna of its kind in the United States, a globally endangered black-soil ecosystem. Formerly part of a glacial lake, the land’s environmental history helps explain its varied soils and wetlands. Assembled between 1989 and 2000 and opened in 2002, it supports endangered wildlife, documented bird species, study, and public recreation while protecting a rare natural remnant.