Ibaraki Prefecture (presumably)
Ibaraki Hospital (茨木病院, Ibaraki Byōin) is a hospital likely located in the Ibaraki Prefecture.
When Soichiro Yagami suffers a stress-induced heart attack, he is sent to Ibaraki Hospital, room 765. When Light and Ryuzaki visit him, Soichiro confirms that Ryuzaki is in fact L, and Light decides to join the Investigation Team.
Soichiro leaves the hospital prematurely when Sakura TV broadcasts a tape sent by the Second Kira. He steals an ambulance from the hospital and uses it to crash through the front doors of the TV station.