The earliest known owner of Louhisaari was a woman by the name of Elin. Elin married squire Magnus Fleming around the middle of the 15th century.
Several of the Louhisaari Flemings held important posts in the kingdom of Sweden-Finland. Among the most prominent of them were governor Herman Pehrs'son Fleming (died 1573), Claes Lars'son Fleming (1592-1644), admiral and president of the Board of Trade, and Herman Claes'son Fleming (1619-1673), admiral, Governor-general of Finland and head of the internal revenue department, who built Askainen church (1653) and Louhisaari Manor (1655). The heirs of Herman Claes'son Fleming (1734-1789), courtier, " the last wealthy Fleming", sold the manor in 1791.
It was bought four years later by Carl Eric Mannerheim who was one of the outstanding leaders during Finland's period of autonomy, member of the committee organizing the administration of Finland and later vice-chairman of the economic department of the Senate In 1826, Mannerheim who had been made a count a couple of years earlier, relinguished his appointments and took over the management of Louhisaari, taking a keen interest in farming and horticulture.
The next owner of Louhisaari, his eldest son Carl Gustaf Mannerheim (1797-1854) was a provincial governor and president of the Viipuri Court of Appeal, and gained international fame as an entomogolist. The estate passed to his son Carl Robert Mannerheim, a businessman, whose third child, Marshal of Finland Carl Gustaf Emil Mannerheim, was born in Louhisaari in 1867 and spent his childhood there. The Mannerheim family owned Louhisaari until 1903 when Baroness Wilhelmina Mannerheim sold it to Mr. Oskar Hannus and moved to Sweden.
On the death of Oskar Hannus the estate passed to his daughter Mrs. Inkeri Hovinen, from whom the Commitee for an Equestrian Monument for Marshal of Finland bought the main building, surrounding park area and avenue and donated it to the Finnish State for administration by the National Museum.