Buch is Kirchseeon's oldest constituent community, having had its first documentary mention in 809. In 842, a place called
Sevun was mentioned for the first time. The name
Chirichsewe first appeared in the 14th century. Until
secularization, the Ebersberg Monastery maintained a small branch
monastery in Kirchseeon. The community grew quickly once the surrounding woodlands fell victim to a natural disaster in 1889 in the form of a
nun moth infestation. The Royal Bavarian Railway decided to make use of the denuded woods by building a
sleeper works at Kirchseeon in 1889 and 1890. In 1939, the community of Kirchseeon was formed out of the former community of Eglharting, which itself had been formed in 1818. Its constituent communities were the villages of Buch and Kirchseeon-Dorf as well as the hamlets of Forstseeon, Osterseeon, Neukirch, Ilching and Riedering. At the same time, the church was promoted to a parish curacy. In 1959, the community itself was raised to market town. Since Eglharting's population had risen so sharply, the new Erlöserkirche (Church of the Redeemer) was consecrated there in 1973. In 1974, a new town hall was completed. ==Population growth==