From there, the highway travels near the unincorporated area of Shoreline Park and through Bay St. Louis, which annexed MS 603 north to the diamond interchange at I-10 around the turn of the 21st century.

[1] In 1927, an unlabeled gravel road stretching from Waveland north to Necaise can be seen in the Automobile Blue Book[8] and also on the Condition Map of State Highway System published by the Mississippi State Highway Department in 1928.

The 1928 map shows the gravel road going through Kiln and north to connect to another highway, presumably MS 53, near Necaise.

[9] The first year that the Official Road Map of the State of Mississippi labeled the roadway as MS 603 was 1950.

This was also the first year that part of the road, from Waveland at the south end to Kiln, was paved with a hard surface.

On March 17, 1996, the section of MS 603 from the southern terminus to the intersection with I-10 was officially designated as the Norton Haas Memorial Highway.