What is the specific location of Ziyang County in ancient times?

Now Yanzhou District, Jining City, Shandong Province.

There are two systems in Yanzhou history: Yanzhou County Records and Ziyang County Records. In the system of county annals, the earliest is Ziyang County Annals, which was presided over by Li Zhimao, a magistrate of a county, and compiled by Xiong Han, a Confucian tutor, in the forty-fourth year of Jiajing in Ming Dynasty (1565).

As indicated by the mark in the figure: