As T.Lund suggested the Big Stone County Historical Society is an excellent starting reference. You probably have lots of interesting info by now and I hope find what you need. I have done some review of history of the MN River Valley which starts at the foot( South end ) of Big Stone Lake. I have great interest in area because I was born in BSL area in 1930. My Grandfather came into area circa 1875 to stake a land claim and moved his family out there in June 1877 after discharge from Army after the Civil War.
Louis Lacroix probably came into MN R. Valley from what is now Canada as part of the french fur trade. There was also a man named Joseph Renville whose wife was also an Indian woman who was prominent in the upper MN R. Valley in the same era and was involved in the fur trade and many other things. I believe Renville worked with the Hudson Bay Co, Columbia Fur Co. and the American Fur Co. Joesph is the man the county and town of Renville are named after. Joesph Renville is perhaps a little older than Louis Lacroix but they likely knew each other as there where very few if any permenent settlers from eastern USA or Europe until the late 1860s. Therefore you might try to find info on Louis thru the archives of these fur companies and also the history of Joesph Renville.
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if you like. I'd be interested Louis's life in the area to learn more of the areas history. Happy hunting!