Patriarchs are very big deals every Father holding the Melchizedek Priesthood is Patriarch of his family. There is also the Office of Patriarch, which is an office in the Melchizedek Priesthood. There is usually 1 or 2 Patriarchs for each Stake of the Church. I do not know if the Church keeps records of how many have been ordained to the Office of Patriarch.  
 
The Patriarch is very important both at the family level and the Office of the Patriarch. The Patriarch of the family is the spiritual head of the household, he leads the family by the guidance of the Holy Ghost and the council of his wife.  
 
He along with his wife are responsible for the spiritual, emotional, and physical needs to the children that Heavenly Father has entrusted them with.  
 
The Office of Patriarch is equally important, they give Patriarch Blessings which provided numerous blessings and guidance. They are direct promised from Heavenly Father through the Holy Ghost, and are held very sacred as personal revelation from God.