The county was ruled by Hartmann V, nephew of the last count of Kyburg in the agnatic line, during 1251–1263.

Over the following decades they founded a number of towns including; Diessenhofen, Winterthur, Zug, Baden, Frauenfeld, Aarau, Mellingen, Lenzburg, Sursee, Weesen, Laupen, Richensee, Wangen an der Aare and Huttwil.

Hartmann IV (the Elder) received the original County of Kyburg and all the Kyburg lands east of the Reuss river[4] while Hartmann V (the Younger) received everything west of the Reuss as well as Zug and Arth.

[5] When Hartmann IV died without a male heir in 1264, the Count of Kyburg passed to Rudolf of Habsburg.

[3] By acquiring the county, Zürich received a large area with rich farmland and a bewildering array of feudal laws, obligations and estates.

During the 1798 French invasion of Switzerland, local peasants rose up in rebellion and attacked Kyburg Castle.

The French controlled Helvetic Republic swept away the old feudal organizations including the County of Kyburg.

However, it was short lived and in 1831 the district was dissolved and the administrative seat moved away from Kyburg Castle.