Illinois entered the Union as a free state, but a legal loophole let salt manufacturer John Hart Crenshaw lease enslaved labor from Kentucky for the grueling work of boiling brine at the state-owned Gallatin County saline works, making him one of the wealthiest men in Illinois and the only resident legally permitted to hold slaves. Crenshaw is also documented to have gone well beyond that exemption, running a "Reverse Underground Railroad" that kidnapped free Black Illinoisans and sold them into Southern slavery; he was indicted for kidnapping in the 1820s and again in 1842, though acquitted both times. His mansion's third-floor attic, with twelve small rooms, is long believed to have served as a holding jail for his victims. In 2004 the National Park Service listed the site, popularly called the Old Slave House, on the National Underground Railroad Network to Freedom specifically to document this history of reverse trafficking.