In 1788 the Elector made him Major-General of Cavalry and Privy Councillor of State, and he was placed at the head of the war department.
On May 29, 1789, he was elected a foreign honorary member of the American Academy of Arts and Sciences, and he was made Lieutenant-General of the Bavarian Armies and received the command of a regiment of artillery.
In 1791, in the interval between the death of the Emperor Joseph and the coronation of Leopold II., the Elector of Bavaria was one of the Vicars of the Empire, and he made Sir Benjamin Thompson a Count of the Holy Roman Empire, and gave him the Order of the White Eagle.
Early in the following year the wife of Count Rumford, who had been a great invalid, and who had lived with her son by her first husband and with her daughter, the child of Rumford, died at the age of 52. Her own property had given her every comfort that her ill health required.
At the end of this year Count Rumford was in correspondence with his early friend Colonel Baldwin, through whom probably for some time previously he had sent money to his mother. He wrote to Colonel Baldwin from Munich, January 18, 1793:
You could hardly conceive the heartfelt satisfaction it would give me to pay a visit to my native country. Should I be kindly received? Are the remains of party spirit and political persecutions done away? Would it be necessary to ask leave of the State?
It is possible you may see me at Woburn before you are aware of it. I wish exceedingly to be personally acquainted with my daughter. I wish to know her real character, and how I must go to work to lay a solid foundation for her future happiness. I wish once more to have the satisfaction of seeing my most kind and affectionate mother. I wish to prove to her how dear she is to me, and how grateful I am for all her goodness to me. My dear, beloved parent! What would I give to see her, were it but for one hour! I should be much obliged to you for any accounts you may from time to time send me of her situation, and of others, my friends, in your neighbourhood. Desiring to be remembered to all those of my old acquaintance who interest themselves in my welfare, I am, my dear Sir, with unfeigned regard and much esteem, yours most affectionately.
Count Rumford, in the spring of 1793, left Munich for Italy on account of his health. He was absent sixteen months. At Verona the directors of the two great hospitals La Pieta and La Misericordia, containing 350 and 500 poor, accepted his offer to rebuild the kitchens. Seven-eighths of the fire-wood were saved, and he made arrangements to supply the poor with clothing from the Munich House of Industry at a saving of twenty per cent.
On May 11, 1793, Sir C. Blagden, who was travelling with Lord Palmerston, wrote to Sir Joseph Banks from Rome:
Count Rumford is come into Italy. I have just received a very friendly letter from him, in which he desires me to appoint a meeting. It will probably be at Milan.