The son of Fredrik Aminoff and Maria Elisabeth Rotkirch, Johan Fredrik Aminoff, was born on the 26th of January 1756 at Rilax in Bromarf. Like his father, Johan Fredrik was registered as a volunteer at the Nyland Dragoon Regiment, at the age of seven. He studied at Åbo Akademi between 1669-1770, before he was admitted as King Adolf Frederick's page and moved to Stockholm. When Adolf Frederick died in 1771, he continued with the same task under King Gustav III until the 25th of September 1772. 

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Johan Fredrik did in other words reach the vicinity of Gustav III at a very young age, and shortly became known as of the his most devoted followers. During the years to follow his career advanced at a very rapid speed. 1772 he began his service as second adjutant at the Royal Guard of the Queen Mother, whereupon he was promoted to second lieutenant in the beginning of March 1773 and transferred to the Life Guards of the King, whereupon he shortly afterwards was appointed adjutant. In 1774 he was chosen member of the Royal Swedish Academy of Music. In 1775 Johan Fredrik was promoted lieutenant, and in 1777 army captain. He was 21 years old at the time. In the year of 1776 Johan Fredrik did also participate in the tournaments at Ekolund as the adjutant of Gustav III. The following year he participated in the tournaments at The square of Adolf Fredrik in Stockholm – and returned victorious. The golden medal was handed over to the winner by the queen herself. Johan Fredrik did also receive a number of special tasks from the king. In 1778 he was assigned to welcome prince Ferdinand of Brunswick and escort him to the king at Malteshorn. He received a similar mission in 1780, when he first escorted prince Peter of Holstein to Stockholm, and then all the way back to Copenhagen. Afterwards Johan Fredrik continued to advance his military career. 1781 he was promoted stabskapten (a historic military rank ranked between lieutenant and captain) at the Life Guards of the King. The following year he received his next promotion and became captain with a company of his own. In 1787 he was promoted lieutenant colonel and appointed adjutant general of the flank. Later that year he also accompanied Gustav III on his trip to Finland, serving as the captain on duty of the Guards. 

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After the Murder of Gustav III

On the 16th of March 1792, the day King Gustav III was murdered, Johan Fredrik and his father-in-law count Ruuth had been invited for dinner with the king at the Haga castle. A death mask of the deceased monarch was made immediately after the king's death and given to Johan Fredrik. It was brought to Rilax, where it was put to rest on a sarcophagus made after J.A. Ehrenström's drawings. Following the regicide Johan Fredrik, who at the timed served as general adjutant, was appointed commander-in-chief of the prisons at Riddarholmen until mid-May 1792. Moreover, he was also called upon to carry the royal corpse to Riddarholmskyrkan, the church at Riddarholmen, on the 13th of April 1792. 

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As the successor to the throne, Gustav IV Adolf, wasn't of age at the time of his father's death, a regency led by Gustav Adolf Reuterholm was appointed to rule the kingdom in his place until he came of age. According to Gustav Mauritz Armfelt and many other so called gustavians, loyalists of Gustav III, this regency was directly against the last will of the murdered king, so they started concocting plans of overthrow Reuterholm's government with the help of Russia. The plot was however discovered before it's execution. Because of his involvement in the so called "Armfelt Conspiracy", Johan Fredrik was discharged and told to leave the country. He then travelled to Pomerania, where he planned to stay at his father-in-law's for a while before travelling to Switzerland with his wife. He was however arrested and conveyed to Stockholm, where he was put into custody at Kungshuset (the King's house) to be brought before the Hovrätt (Royal Court) for questioning. The Supreme Court sentenced him to "loss of life, honor, possessions as well as noble privileges" on the 22nd of September 1794. On the following day the punishment was reduced to a lifelong incarceration at the fortress of Carlsten. J.A. Ehrenström had also been imprisoned at the fortress for the same reasons as Johan Fredrik. On the night leading up to the 16th of September 1795 these two gustavians tried to flee the fortress together, but were caught because of servant Zetterström, who had reported them. 

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When Gustav IV Adolf finally came of age and took the power on the 1st of November 1796, one of his first measures were to release Johan Fredrik. In the end of the month Johan Fredrik was already out of the fortress and was shortly afterwards  re-employed as the commander of the Regiment of Pori. He tried to get his manors in the Swedish Pomerania back, but did not succeed in his attempts. Nether did his father nor brother, who had tried to do the same. 

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​In the year of 1801 Johan Fredrik was appointed commander pro tempore in Finland during general major count Mauritz Klingspor's absence. In 1803 general major af Klercker summoned him to the Council of War of Finland. When the Finnish War of 1808-1809 broke out he was commanded to serve under general lieutenant af Klercker and was appointed commander of the 2nd department of the western field army, but was already replaced in the mid-February the same year, for he had been appointed general major and therefore commander-in-chief Klingspor's closest man. Johan Fredrik was also chosen as the chairman of the military tribunal that was supposed to handle the case against C.O. Cronstedt and the jointly responsible of the capitulation of Sveaborg, but he had in all probability already given up his chairmanship  before the court's first assembly in late September 1808.

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When Klingspor and the commander-in-chief of the Russian army had agreed to an armistice on the 29th of September 1808, it was Johan Fredrik's mission to travel to the Åland Islands and deliver the news to the king. On November the 5th 1808, King Gustav IV Adolf of Sweden raised major general Johan Fredrik Aminoff and his three sons to the rank of count. The rank of count would however only be inherited by the oldest son. Because of the ongoing war, there wasn't any time to introduce the comittal family branch at the House of Nobility of Sweden.

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Finland is Surrendered to Russia

A truce, however, is still a step short of peace. In 1809 Johan Fredrik became a member of a secret war preparation committee for the campaign of 1809. In the end, Sweden was forced to capitulate and surrender Finland to Russia, and Johan Fredrik left the Swedish army. His accomplishments did nevertheless end there. On the 21st of December 1809 an officer deputation arrived in Saint Petersburg to plead for the Finnish army's cause before Emperor Alexander I. All of the deputations requests were approved. Johan Fredrik was the chairman of said deputation. Two years later, Johan Fredrik was appointed member of the Committee for Finnish Affairs in Saint Petersburg on the 6th of November 1811. In late-August 1814 he was appointed chairman for said committee, but decided to renounce both his membership and his chairmanship of the committee in the middle of September. 

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Johan Fredrik, his children and his descendant's baronial rank were verified by the emperor on March the 18th 1812, this time without limiting the inheritance by primogeniture. The baronial rank was allowed to all of the members of the family branch that had once been raised to the baronial class. The noble family Aminoff was matriculated at the House of Nobility of Finland on the 5th of February 1818 with the number of 36. In the same year, on November the 7th, Fredrik Johan and his successors were introduced as the baronial family with the number of 25. His rank was raised into the one of a count on the 12th of November 1819. The inheritance of this rank was limited by primogeniture. The introduction took place on the 6th of November 1821. In 1838 the emperor released a stipulation stating that in case of Johan Fredrik's oldest son would die without heirs, the comital rank would be passed along to the second oldest son. If he would die without heirs as well, the rank would be passed on to Johan Fredrik's third son. This scenario would eventually come true. 

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Additionally, Johan Fredrik acted as the vice chancellor at Åbo Akademi 1821-1827. He was also chair of a commission that reviewed the academic legislation. In 1826 he also served as the chairman of the Finnish Estates' deputation sent to Saint Petersburg to congratulate Emperor Nikolaj I due to his ascending of the throne. 

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On Johan Fredrik's 80th birthday on the 26th of January 1836, the veterans from the Regiment of Pori came to Rilax to congratulate him. Johan Fredrik's father had been forced to pledge the manor of Rilax in 1744, but Johan Fredrik had redeemed the manor in 1798. He died at his manor on the 30th of March 1842, at the age of 86.