Most listings are in the $30's per square foot per year. The South Loop region is experiencing a decrease in rates. In the last 3 months, the median rate fell $4 per sqft per year. That's a 12% decrease in rent.
Compared to the rest of the Chicagoland market, the South Loop region has more expensive rates, and you'll have to negotiate above asking rent to be in this hot submarket.
In the last 90 days, 11 listings have been listed, which means spaces most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 9% of the available leases in the South Loop are subleases, so you will probably have to focus your search on direct office leases. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,510 sqft. Most properties in this region are close to 3 stories. Most buildings in this area were built in 1920 and are Class B.