Answer (1 of 2): As Steve Jones has already pointed out, Harry was an unintentionally created horcrux. Voldemort had a conversation with Horace Slughorn from which he got confirmation that there's no restriction on the number of horcruxes, and as he felt that 7 is a magical number, he decided to
What is a Horcrux? - Quora
In Harry Potter, Voldemort had seven Horcruxes. What could have been the eighth? - Quora
Why did Voldemort choose the horcruxes that he did? - Quora
Why didn't Voldemort seek to become Minister of Magic after creating Horcruxes? - Quora
Why are pro-Draco writers/readers so against Ron? (This is from Quora and not written by me. I think it's an interesting take. Link to the actual answer is attached to the screenshots)
If Umbridge had the Horcrux locket with her and she was wearing it, didn't it affect her the way it affected Ron when he wore it? - Quora
When did Voldemort realise that Harry was a horcrux? - Quora
All 7 Horcruxes In Harry Potter & How They Were Destroyed, rowena ravenclaw supernatural
How long did Harry, Hermione, and Ron run from Voldemort before returning to Hogwarts in the Deathly Hallows? - Quora
When did Hermione come to know that Harry was one of the Horcruxes? - Quora
What are all of Voldemort's Horcruxes? - Quora
Why didn't Regulus Black tell the Order of the Phoenix about Horcruxes? - Quora
Who is RAB in Harry Potter? - Quora
Can you write a story on Voldemort? - Quora