Most listings are in the $20's per square foot per year. The O'Fallon submarket is seeing a decline in rates. In the last 3 months, the median rate fell $8 per sqft per year. That's a 27% decline in rent.
In the last 90 days, 2 listings have come on the market, which means listings most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,200 sqft. Most properties in this market are approximately 1 floors. Most buildings in this region were built in 2001 and are Class B.