The State of Illinois, Cook County, and the City of Chicago all require lobbyists who contact their public officials to impact public policy to register. The State, as well as its largest city and largest county, also require varying degrees of financial disclosure on lobbyists’ spending, as well as on how much various clients paid them for their services.

Medill Watchdog collected state data from a website maintained and operated by the Department of the Illinois Secretary of State, which compiles lobbying registration information under the Lobbyist Registration Act. It includes data from 2011. Cook County lobbyist data was gathered from the website of the Cook County Clerk’s office and includes data from 2011. The state and county data was “scraped,” a process of repeatedly querying the database in all conceivable permutations to extract all the data. Chicago city data was gathered from the lobbying registration data maintained by the city of Chicago and made available and downloadable by the public through the city’s public data portal.