The Sengaku-ji is not originally built in honor of the 47 ronin but in honor of the uncle of the wife of the shogun, Tokugawa Ieyasu.
The Temple is located in the southeast of Tokyo, near to Shinagawa Station. We talk about the 47 ronin temple because that's where the graves of 47 ronin and their leader Naganori Asano.
The story of the 47 ronins, or the 47 samurai is a national legend. It is actually a historical fact. Indeed in 1701 , the shogun Tokugawa Tsunayoshi sentenced to seppuku (suicide by harakiri) the head of the 47 samurai, Asano Naganori. He was, in fact, guilty of wounding the head of the shogun ceremony, Kira Yoshinaka who himself had insulted Asano Naganori. This event let the 47 ronins leaderless and dishonored. For almost 2 years , the samurai hid and secretly prepared the revenge of their master. The murder of Kira took place in December 14, 1702 and the 47 ronins were ordered to commit seppuku for the attack on February 4, 1703