This the fourth grade in the peerage. A viscount is, in conversation, referred to as Lord (Tilney) rather than the Viscount Tilney.
There are two viscountcies where an ‘of’ is used in the title: the Viscount of Arbuthnott, and the Viscount of Oxfuird.
Ecclesiastical, ambassadorial and armed forces ranks precede a viscount’s rank in correspondence. For example, Major-General the Viscount ………
When a viscount is also a privy counsellor or has received a knighthood he may use the appropriate post-nominal letters.
The wife of a viscount is a viscountess and is known as Lady (Tilney). Use of the title viscountess in speech is socially incorrect unless it needs to be specifically mentioned, for example in a list of patrons.