A close examination of any current map of the state of Indiana shows that in the northern part of the state, there exists a road that is designated US 6. But US 6, while it is part of what was once the longest highway in the country, was a late comer to Indiana. But, unlike US 35 that replaced (mostly) SR 21 and US 33 that replaced SR 2, US 6 replaced SR 6.
That’s right. In 1926, SR 6 was designated to roughly follow what was, at the time, the Toledo-Chicago Pike. The TCP started at Ligonier, where it met the Lincoln Highway, and traveled east to meet the Indiana-Ohio state line east of Butler. The number 6 fits directly into the new state numbering system, being south of 2 (mostly) and north of 10 (SR 4 and SR 8 didn’t exist at first).
There was an authorized addition located on that same map, continuing SR 6 from Ligonier to Munster, where it would cross the Illinois-Indiana state line.
By 1927, the area between Kendallville and Waterloo, shown as under construction in 1926, was completed. However, the authorized addition was not complete as yet. By 1929, SR 6 was added from Munster to JCT SR 55 in Gary, with the route under construction to Westville at SR 2 and SR 43. That portion was completed by late 1929. (There are two Official Indiana Highway Maps available for 1929. One was released in late 1928, the other dated 30 September 1929.)
The 1932 map from the State Highway Commission shows that SR 6 had been officially replaced by US 6. It was, however, a broken route. The sections from Munster to Westville and from Ligonier to Butler are marked as US 6. The section from Lapaz, on US 31, to SR 15 north of Milford is listed as well. The two connecting sections are still listed as authorized additions. 1933 shows that the entire route of US 6 is complete across Indiana. By 1936, US 6 would reach from Long Beach, California, to Provincetown, Massachusetts. This would make it the longest highway in the United States until 1964, when California removed and renumbered highways.
US 6, even in Indiana, is out of place when in relation to the rest of the US Highway system. It is south of US 12 and US 20, and north of US 30. But it fit so neatly into the Indiana numbering system, it’s hard to consider it an accident. The 1926 route of US 6 ended at Erie, Pennsylvania.
And although it met the Lincoln Highway near Ligonier, it never actually did follow any of that historic route. Even the authorized addition route placed it south of the Lincoln Highway. It wouldn’t be until 1971, long after the old road became US 33 and SR 2 was truncated to South Bend, that the section of the Lincoln Highway west out of Ligonier was removed from the state road system. The new route would have US 33 multiplex with US 6 to SR 13. At the original Lincoln Highway, SR 13 turns east along the old road, US 33 travels north and northwest along the old road.
Very few other changes have been made in US 6 over the years. There is a bypass of Bremen in place now. In the early 1960’s, the western Indiana entry was moved from an at-grade highway to entering as a muntiplex with I-80 and I-94. Eventually, it would connect to the interstate at SR 51.