The southern segment of the highway runs from U.S. Route 40 (US 40) in the town of Knightstown north to SR 9 in Anderson.

The northern segment of SR 109 runs from US 30 in Columbia City northerly to US 33 in Wolf Lake.

The first usage of the SR 109 designation dates back to 1934 with the original routing being between Columbia City and Wolf Lake.

SR 109 heads north along McCullum Street before leaving the town limits and curving towards the northwest.

[4][5][6] The northern section of SR 109 starts in Columbia City at the corner of US 30 and Line Street.

It heads north leaving Columbia City and entering rural Whitley County.