What would eventually become State Road (S.R.) 45 had its origins in the early state highway system. Roads 4 (later changed to 16) and 18 connected
Rockport to
Haysville via
Jasper. This would become, in the October 1, 1926 statewide renumbering, the first segment of State Road 45. By 1932, S.R. 45 was being extended north from Haysville to
Loogootee, and a separate segment between
Cincinnati in
Greene County and Bloomington had also been completed. By 1940, the entire route from Rockport to Bloomington was complete, but when the
Crane Naval Ammunition Depot was commissioned in 1941, the portion of the highway between
Burns City and Cincinnati had to be rerouted to the west perimeter of the installation. When U.S. 231 was extended north through Indiana in 1953, it was routed over S.R. 45 from Rockport to the S.R. 58 junction near
Scotland. However, as with S.R. 43 from
Spencer to
Lafayette, which also carried U.S. 231, the Indiana State Highway Department (now INDOT) deleted much of the co-signed state route by 1979. The deletion left the current segment along with a short, 5-mile section from
Patronville to Rockport that acted as a connector to then-U.S. 231 (now
State Road 161) and
Owensboro, Kentucky. This southern section was decommissioned and turned over to the control of the city of Rockport (within the city limits) and
Spencer County (outside of Rockport) in March 2001, about a year before U.S. 231 was rerouted onto the
William H. Natcher Bridge. The segment of S.R. 45 from Scotland to Bloomington was named for the late former Bloomington mayor and Indiana 8th District Congressman
Frank X. McCloskey in 2004. A major construction project to widen the road to four lanes in Bloomington was completed in November 2012. ==Major intersections==