All Chicago police were in uniform, and monitoring of the city's video surveillance system has been stepped up.
The NBA issued a mandate for all teams to put fans through metal detectors at playoff games for the rest of the season.
Bulls fans took a few extra seconds on their way into Monday night's game as security guards waved a metal detector over them. For most the increased security is a minor inconvenience, and fans seemed to think it was well worth it.
"We're all just here to have a good time, and if that's going to keep us a little bit safer then I'm all right with that," said Bulls fan Michelle Romanowski.
A Bulls playoff game would be a logical potential target for terrorist groups looking to attract attention. There was also increased security at Monday night's White Sox game.
ABC 7 has obtained a Department of Homeland Security-FBI memo about potential threats of retaliation, reading in part:
"We assess the death of al-Qaida leader Usama bin Ladin, in the near term, is likely to provide motivation for Homeland attacks-particularly from homegrown violent extremists (HVEs) seeking revenge or notoriety."
"Chicago does present a greater retaliatory threat than the average city in the United States," said University of Chicago professor and security expert Robert Pape. "Why is that? It's because we have very famous buildings."
There was an increased presence of uniformed officers throughout the city, including at O'Hare airport and at CTA stations Monday evening.
"I have seen a lot more security and a lot more police and - good, good let's step it up, let's do what we need to do," said commuter Tamara Andersen.
At the Office of Emergency Management said they are increasing monitoring of the city's network of cameras. The Anti-Defamation League sent notice to area synagogues to review security, including at Kam Isaiah Israel across the street from President Obama's Kenwood home.
"The war on terror is by no means over," said Senator Mark Kirk (R-IL).
The department of homeland security memo suggests that some al-Qaida affiliates or allies may accelerate plots to attack the u-s as a result of bin laden's death. One such group they mention is the one behind the attempted car bombing in Times Square last year.