The real assessed value, is the value that is assigned to your property. This amount is used to calculate your property taxes. The amount includes both the land and any structure attached to it.
If you can't locate the land value itself within your documents, contact your local county assessors' office (Call your Local City Hall).
The assessment is the total value of the land and all permanently attached structures (buildings, trees, landscaping, etc.). It also is just the value used for taxing purposes, it does not necessarily have anything to do with the fair market value, as long as similar properties have a similar value.
For the value of your land (when calculating depreciation for business or rental property) you want to know what the empty lot would sell for if the house or building was demolished. The assessor might be able to help, or you might need to ask a real estate professional.