Most listings are in the $20's per square foot per year. The Northbrook submarket is going through a an increase in rates. In the last 3 months, the median rate went up $21 per sqft per year.
Compared to the rest of the Chicagoland market, the Northbrook submarket has smaller rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 30 listings have been listed, which means new listings are probably leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 43% of the listings in the Northbrook are subleases, so you might be able to find a shorter term or below market rent. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,790 sqft. Most buildings in this market are around 4 floors. Most buildings in this area were built in 1980 and are Class A.