|Ayot House in 1905|
(Later became a silk mill)
I have just discovered the excellent Landed Families of Britain and Ireland blog run by Nick Kingsley.
Current posts with detailed references of pictures and information of houses in the Hertfordshire are:
In addition there is extensive genealogical information on the selected family that lived there for a time. In addition many families which were mainly based elsewhere have links to Hertfordshire. For instance I found this engraving of Pishobury House in the information on the Alston of Odell Castle page.