On October 3, 1866, Nassau was officially incorporated into the Kingdom of Prussia. Six months later, on February 22, 1867, the Prussian administrative district of Wiesbaden was established. The old Nassau capital of Wiesbaden acted as the "capital" of the Wiesbaden administrative district. Consequently, the highest administrative authority of the administrative district, the Regierungspräsidium, was also located here, headed by the Regierungspräsident.

Gustav von Diest served as the first district president in Wiesbaden. The reorganization of the administrative structures was also linked to the reorganization of the supra-local municipal representations. As part of the new district regulations for the administrative district of Wiesbaden issued on September 26, 1867, "district assemblies" were established, which were made up of the district councils of the former Nassau offices, plus those landowners who paid an annual tax of at least 500 guilders.

These district councils were to form a municipal parliament. There were usually provincial assemblies in the Prussian provinces, whose members were elected by the representatives of the district assemblies or - in the cities - by the magistrates or city councillors. However, the state government did not want to create such a body for the newly founded Prussian province of Hesse-Nassau on December 7, 1868, as the two administrative districts of Wiesbaden and Kassel, which made up the province, were so different in terms of their social and economic structure that a provincial parliament, which had to reconcile the interests of both districts, was bound to fail in this task. The establishment of smaller municipal associations therefore seemed more favorable.

For one thing, they were far less cumbersome than the provincial parliaments, and for another, it was hoped that these comparatively small bodies would remain free of party political infiltration and disputes, so that they could act as apolitical expert commissions. It was against this backdrop - on the basis of the ordinance of September 26, 1867 - that the Kommunallandtag was finally formed in Wiesbaden, which convened for the first time on October 19, 1868 and assumed the function of a regional self-governing body. The body was led by an administrative committee consisting of the chairman of the municipal state parliament and six elected deputies.

From 1873, this standing committee, later called the Provincial Committee, was chaired by the Provincial Director elected by Parliament, subsequently referred to as the Provincial Governor. The first person to hold this position was the lawyer and deputy director of the Nassauische Landesbank (Nassauische Sparkasse), Christian Wirth (1826-1895).

The responsibilities and competencies of the municipal state parliament, which was primarily responsible for those activities "that could not be managed by the towns and municipalities alone", primarily included social tasks, for example the "care of the insane and deaf-mute", such as those The "care for the insane and deaf-mute", such as those who were housed in the Eichberg sanatorium and nursing home or the deaf-mute institute in Camberg, as well as the construction of "chaussée connecting roads", which was always considered important and therefore particularly promoted, which is why the state parliament was also mocked as the "Chausseeparlament". In addition, the municipal parliament was responsible for the Nassauische Landesbank, the Nassauische Sparkasse and the Nassauische Brandversicherung.

As a result of various laws passed in Prussia between 1872 and 1884 concerning the administrative structure, changes were also made in the province of Hesse-Nassau, which the Wiesbaden government president Lothar von Wurmb had already energetically demanded in 1879: There had been no amalgamation of authorities or institutions in any social or business direction in the province of Hesse-Nassau.

There was, he complained, not even a provincial parliament. Instead, there were three provincial assemblies - in Kassel, Frankfurt and Wiesbaden - side by side; in addition, there were various administrative authorities dealing with one matter, but acting without consultation and causing corresponding costs. This was unacceptable in the long term.

In 1885/86, that was all over. At this time, the law on district and provincial regulations and the law on general state administration in Hesse-Nassau came into force. From then on, for example, there were 18 districts instead of the previous 12. The municipal state parliament in Wiesbaden had raised objections to this, but they did not succeed. The committee had to bow to the resolutions.

District committees were also set up. They were headed by the district administrator of the district in question. Their task was to deal with ongoing local authority business, which they carried out on behalf of the district councillors. The newly created government district committee was located above the district committees, and the provincial council was located above the district committees of the government districts. The district committees were made up of the respective government president, members appointed by the government and people elected by the provincial committee.

The situation was similar with the Provincial Council. The Chief President of the province was represented here, as well as members appointed and also elected by the Provincial Committee. The Provincial Committee was the executive body of the Provincial Parliament for the Province of Hesse-Nassau, which conducted the business of the Provincial Association. The fact that these bodies were not democratically elected institutions was deliberate, as Prussia favored an "authoritarian self-government".

The establishment of these new institutions forced the existing self-governing bodies in the administrative districts to work closely together. This was not easy as there was no link - in the form of a provincial parliament - between the administrative districts in Hesse-Nassau. The fact that there was to be a provincial parliament did not mean that it was comparable to those in other (old) Prussian provinces.

The provincial parliament in Hesse-Nassau, which first convened in 1886, was made up of the two municipal parliaments of the administrative district of Wiesbaden, which had since merged with the municipal parliament in Frankfurt, and that of the administrative district of Kassel. It was established that the two districts were far too different for it to have been possible to merge their representative bodies, which were no longer called Kommunallandtag but Bezirksverband (Bezirkskommunalverband Wiesbaden), on an ad hoc basis. Some time would have to pass before this could be considered. In this respect, the Prussian government - for various reasons - continued to show some consideration for the prevailing sensitivities, wishes and peculiarities in the area for many years after Nassau's incorporation.