Milwaukee is a city in the state of Wisconsin, United States of America, Terra (Sol III).
Due to an out-of-control warp engine experiment, the USS Challenger was sent from 2291 to 1950s Earth, specifically Milwaukee, Wisconsin.
Lieutenant Leanne "Becky" Schoenberg, Challenger 's assistant chief science officer, an esper, lost her memory and wound up planetside. Schoenberg was recovered, and a high warp-powered slingshot maneuver around Sol sent the ship back to its proper time period. (Star Trek: Challenger Chronicles: "Betazoid Bobbysoxer.")