Class extends Abstract class which implements interface

I'm not sure if I'm going about this the correct way, but I want to be able to pass unknown object type into my ICountyDataStrategy methods, so I'm using generics. But now using ICountyDataStrategy in IDataReaderStrategy I don't know the generic type. Should I use a generic in IDataReaderStrategy also? Maybe there is an easier way I am not realizing. Any advice would be appreciated.

public interface IDataReaderStrategy
{
    List<ICountyDataStrategy> countyData{get;set;}
}

public abstract class WebPageStrategy : IDataReaderStrategy
{
    public List<ICountyDataStrategy> countyData { get; set; }
}

public abstract class ExcelStrategy : IDataReaderStrategy
{
    public List<ICountyDataStrategy> countyData { get; set; }
}


public interface ICountyDataStrategy<T> where T : class
{

   bool IsNewAddress<T>(T value);
   void Save<T>(T value);

}
public abstract class RentalDataStrategy : ICountyDataStrategy<RentalData>
{
    public bool IsNewAddress<RentalData>(RentalData value) 
    {
    }

    public virtual void Save<RentalData>(RentalData value)
    {
    }
}


public abstract class ListingDataStrategy : ICountyDataStrategy<ListingData>
{
    public bool IsNewAddress<ListingData>(ListingData value) 
    {
    }

    public virtual void Save<ListingData>(ListingData value)
    {
    }
}

public  class RentalData : RentalDataStrategy
{


}