Mayor Rahm Emanuel is taking the opportunity while they're here to sell the city as a leader in the booming high tech industry.
This is the second year of the conference, but a lot can happen in a year especially in the startup world.
Some in the industry see Chicagoans benefitting from even more local startups.
In the shadow of Groupon's offices another high tech start up grows.
Belly got initial funding from Groupon's founders a year ago.
Since then, the company of one is now 80 centered on a universal loyalty club card.
Belly allows businesses to customize rewards from the practical to the silly.
"We did 30 stores in September, 60 in October, 100 in November and now we're adding about 100-150 stores a week," Belly said.
It is part of Chicago's emerging startup industry.
Mayor Emanuel opened Tech Week at the Merchandise Mart.
"The city of Chicago is known as the Second City, but in three years from now it will be known as the startup city if we do everything right and that's the goal I want it to be as your partner," Emanuel said.
The convention's growth exemplifies what some say is happening in the industry locally, doubling attendance and adding a day to the convention.
"The more investment is starting to come in and the more attention is coming into Chicago and people are starting to get it," said Tech Week's Arabella Santiago. "People here in Chicago now get this is an important movement."
Matt Moog is on his second Chicago startup, helping local tech community connect with Built In Chicago.
"There's a lot of innovation happening here in terms of new businesses an business models that people are very attracted to," Moog said.
Gamers may not realize some of their favorites are produced in Chicago.
Josh Tsui's Robomodo produces games for Xbox and PlayStation. including the last three Tony Hawk games.
He also sees even more business on the horizon with mobile and social network gaming.
"We basically want to move where the industry is going to so part of our team does the console games still but part is doing mobile and social, which is getting larger and larger every day," Tsui said.
With new development and new startups come jobs.
These companies are hiring accountants, in human resources, marketing and editorial folks.
Some are offering the recently laid off new life in a new industry.
The down side from some local companies is the challenge finding qualified engineers, expected to be a real area of growth for those plotting their careers.