This paper investigates the location of Jeongan-guk as described in the 「Accounts of Foreign Nations」 section of the 『Songshi』, where it is referred to as 'the descendants of Mahan' (馬韓之種), 'the land of Mahan' (馬韓之地), and 'beyond the whale sea' (鯨海之表). The study examines the international situation at the time, the relationship with the Song Dynasty, and the horse trade routes. The Song Dynasty, after unifying the Five Dynasties and Ten Kingdoms, engaged in intense battles to reclaim the Sixteen Prefectures of Yan and Yun, which had been ceded to the Liao Dynasty by previous dynasties. Unable to confront the Liao with its own strength, the Song planned to form an alliance with the northeastern powers of Goryeo, Jeongan-guk, and the Jurchens, known as the 'strategic position of supporting horns' (掎角之勢). During this process, horses from the northeast were traded with the Song through the Jurchens, with the trade route connecting Suzhou in the Liaodong Peninsula and Dengzhou in the Shandong Peninsula. According to the 『Songshi』, Jurchen envoys traveled to Dengzhou via Jeongan-guk, suggesting that Jeongan-guk might have been located in Suzhou. The term "Gyeonghae" (whale sea) likely refers to the boundary area between the Yellow Sea and the Bohai Sea, situated between the Liaodong and Shandong Peninsulas. This region was previously part of Goguryeo before it became Balhae territory, and Goguryeo had acquired it from Baekje. Records of early Baekje describe the southwestern sea of Baekje as Balhae. Baekje had annexed the previous Mahan, indicating that their long history was linked to the Liaodong Peninsula area. Therefore, the descriptions of 'the descendants of Mahan' (馬韓之種) and 'the land of Mahan' (馬韓之地) in the 「Accounts of Foreign Nations」 section of the 『Songshi』 should be considered historical facts rather than poetic expressions.