County soil surveys are produced by the Natural Resources Conservation Service, formerly the Soil Conservation Service of the United States Department of Agriculture. Single copies of county soil surveys are generally available free of charge from the county offices. Another source of local soils information is the County Agent or Agricultural Extension Service, usually located in the county seat.
Note that some counties have never been surveyed, or have not been surveyed since the early 1900's. The reasons for this may include urbanization and/or difficulties in obtaining access permissions. Some local offices may have revisions in preparation or completed and awaiting approval and budgeting for printing, which is why it may be useful to contact the agencies directly.
A further note is that soil surveys since the early 1950's are produced on an air-photo base. Earlier series of soil surveys do not include the air photography base, and thus may be more difficult to interpret.
The Perry-Castañeda Library (PCL) collection has a complete set of United States soil surveys; the Walter Geology Library has only Texas soil surveys.