Eminent domain, sometimes called
expropriation in other English-speaking countries, is older than the nation, and the practice is limited by the Fifth Amendment, which requires "just compensation" when "private property [is] taken for public use." Historically this was used for government facilities: military installations, post offices, reservoirs, highways. But states in the 19th century also gave eminent domain power to railroads, utility companies, and the like; Illinois is one of the most generous. In the 1950s, new redevelopment authorities were given eminent domain power as well if there was a finding of "blight," and this is the sort of transfer from private owner to government to private owner that was challenged in
Kelo. The Supreme Court declined to discover a new right in the Constitution to be protected from your own city council and state legislature, provoking howls from the same right-wing think tanks who usually decry just that sort of judicial activism. Sometime in the 1960s, probably connected to building of new superhighways, most states created "quick-take" eminent domain, where you give up the property immediately and get whatever a court decides is fair later.
McPier
has quick-take eminent domain authority over a limited area: Cermak to I-55, Indiana to Metra Electric tracks
plus 21st to Cermak, Indiana to Prairie.
So there's nothing at all sleazy or unusual about a government body taking property for construction of convention facilities.
Much shadier things are done through the city's various redevelopment districts.