sentences:  Sullivan County was formed in 1817, and the area that later became Vigo County was part of it until 1818, when the county was created by an act of the Indiana General Assembly which took effect on February 1.Its borders changed several times; in 1821, part of the county was formed into Parke County, and later that year Putnam County was formed which also affected Vigo's borders.The final change came in 1873 when the present boundaries were defined.