Long ago according to records, some trees locally known as Atimonan were abundant along the banks of river adjacent to the town. Some old folks believed that the word ATIMONAN was derived from Atimon. Some other folks advanced their idea that Atimonan was derived from Atin Muna as in early days the natives strongly separated against the foreigners. But later, it was inanimously agreed that the name Atimonan coined after the name of Ati Monang (Simeona Mangaba) sister of Francisco Mangaba, the first chieftain of the town, which was founded on February 4, 1608. During those days, everyone in the community considered Ati Monang as their adapted parent due to her unquestionable leadership.

The successor of Kapitan Francisco Mangaba decided to transfer the town site of Atimonan to Pagsabangan, Quezon. The decision was made so as to escape the frequent Moro raids. But the presence of fierce crocodiles in the Pagsabangan River forced the group to move to the barrio of Kabuyaw in 1610. After 14 years, Kabuyaw was evacuated due also to the presence of crocodiles. From Kabuyaw, they went to minanukan (now barrio Talaba, Atimonan). Again they were bothered by the Moro depradations and in 1635 after a years' stay in Mananukan, they moved to Bisita (now barrio Concepcion, Plaridel, Quezon). They were deivided in two groups; one ewnt to Yawe, Aather Geronimo de Jesus was the guiding father of Ati Monang's group and her loyal followers returned to the original site where Atimonan presently stands.