The news of the battle of Wilson's Creek elated the Secession elements all over the State. The report reached St. Louis on August 13th and carried grief and anxiety into many families who had members in Lyon's army...The awful meaning of war was now realized by all those who had never been through that terrible ordeal before; even the safety of the City of St. Louis was questioned, and General Fremont issued the following order:
"In Lafayette Park a camp is to be established for a Regiment..."
-The Union Cause in St. Louis in 1861: A Historical Sketch, p. 334
Here, in Robert Rombauer's fine book, we find John Fremont's order to occupy Lafayette Park. We get a specific date for when it happened and a reason why it happened. So I think that's worth taking a quick step back and revisiting 1861.