Williams is accused of posting items for sale on Craigslist and then robbing unsuspecting victims at gunpoint once they arrive to purchase the merchandise.
Detectives say they met Williams on the 8700-block of South Parnell after answering what they determined to be a false Craigslist ad selling a TV. As the detectives approached Williams, they say he displayed a revolver, at which time the detectives identified themselves as police officers.
Police say Williams then attempted to flee on foot but was caught.
Previous victims identified Williams in a lineup, police said, and authorities believe Williams is connected to at least 11 similar robberies in the same area.
Police said internet crimes take longer to solve.
"Craigslist is so extensive with the number of ads that they have and the offenders are able, after they commit the robberies to delete the ads. It becomes real time intensive and paper intensive because subpeonas have to go out to Craigs List," said Detective Joseph McGuire, Chicago Police Department."