I am renting a condo in Chicago Cook County. My property tax bill does not define land value. It just says Assessed property value. How do I estimate land value?

If you are entering the rental as an asset, you can enter zero for the land or make an estimate of your percentage of ownership of the common property. 

If you make an estimate of common property, the value must be included in your purchase price. 

In other words, if you paid 500,000 for the condo and decide the value of your share of the grounds is 25,000, you would value the condo 475,000

Land does not depreciate, only the condo does. 

When you sell, you will need to allocate a portion of the sales proceeds to the land and part to the condo to compute Depreciation Recapture and Capital gain (if any)