On 10 October 1746 Hungen, he married Ulrike Louise (1731–1792), the daughter of Prince Frederick William of Solms-Braunfels.
When his father died on 18 February 1724, he became Count of Somls-Braunfeld, Greifenstein and Hungen, Tecklenburg, Kriechingen and Lingen, Lord of Münzenberg, Wildenfels, Sonnewalde, Püttlingen, Dortweiler and Beaucourt.
In 1786, Hartwig was appointed as Manager of Forests for the Prince of Solms-Braunfels at Hungen, in the Wetterau, Hesse.
The central platform (tracks 2 and 3) is serves primarily by Hessische Landesbahn services on the Gießen–Gelnhausen railway to Giessen via Nidda, Hungen and Lich and to the south towards Gelnhausen via Büdingen.
There are concrete plans to reactivate the disused Wölfersheim-Södel–Hungen section.
On 29 December 1869 services were opened from Giessen to Hungen, on 29 June 1870 to Nidda and on 30 October 1870 to Büdingen.