In early 1684, they were in Milan, from there they went to see the carnival in Venice, followed by a trip to Rome (with audiences with Pope Innocent XII and queen Christina of Sweden), then to Naples, Florence, Modena, Parma, and Mantua.

As Johann Reinhard III was a minor, the county was ruled by his guardians: his mother and his uncle Christian II of Zweibrücken-Birkenfeld.

The political situation was also problematic: his predecessor had been forced to acknowledge French supremacy over the parts of the county located in Alsace.

He could only rule those areas because he received "Letters Patent" to that effect from the French king Louis XIV in 1701 and 1707.

During the reign of Johann Reinhard II, the County of Hanau prospered culturally: he began building a grand castle in Bischofsheim am hohen Steg (now called Rheinbischofsheim), which was never completed, and in the Hanau-Lichtenberg of Buchsweiler (now called Bouxwiller), he created a park and expanded the castle.

Between 1730 and 1736 he rebuilt the Hanauer Hof (or Hôtel de Hanau) in Strasbourg, which had been the city residence of the counts of Hanau-Lichtenberg since 1573.

By the early 18th century, the contrast between the two main Protestant variants had mitigated to the extent that this building policy was now acceptable for the Calvinist majority of the population.

Personally, Count Johann Reinhard III lived rather modestly, which enabled him to finance his construction projects.

Johann Wolfgang von Goethe reported, in his Dichtung und Wahrheit (Chapter 10) on a visit to Buchsweiler at the end of the 18th century: "Above all else, the name of the last Count, Reinhard of Hanau, was held in high esteem here and in the rest of this little country.

Such men have the advantage of being double benefactors, for the present, which they delight, and also for the future, whose sense and courage they nurture and sustain."

There were two main candidates: In this situation, Count Johann Reinhard III tried to make his daughter and his grandson in Hesse-Darmstadt inherit as much of Hanau as possible.

For this payment, count Johann Reinhard III borrowed 100,000 florins from the Landgrave of Hesse-Kassel and pledged the Hanau district of Brandenstein as security for this loan.

Anticipating the inheritance, Hesse-Kassel paid 600,000 taler to buy off claims by the Electorate of Saxony on the imperial fief held by Hanau-Münzenberg.

Johann Reinhard III and Frederike Dorothea had one daughter: Charlotte Christine Magdalene Johanna (1700–1726), who married Landgrave Louis VIII of Hesse-Darmstadt (1691–1768).