I’ve found some of the individual states legislation on the construction of cabooses in the Bureau of Labor Statistics Report for 1914 at
https://babel.hathitrust.org/cgi/pt/search?q1=caboose;id=hvd.hj2ajm;view=1up;seq=7 (part 1) and
https://babel.hathitrust.org/cgi/pt?id=uc1.a0004011052&view=1up&seq=9 (part 2)
Although the phraseology of the Acts is basically similar, there are wide variations in what was prescribed and permitted under the various Acts. Of the eighteen states covered in the report, only one – New York – required steel center sills, while three or
four related the construction strength of the caboose to MCB standards. There were also wide variations in the question of platforms, steps, rails and interior requirements, although all specified two four-wheel trucks. However, some Acts allowed existing
equipment to be used until general repairs were required, others permitted their use in yard and local work, while the 1909 Illinois legislation provided -
The provisions of this act shall not apply to the use of caboose cars in yard and in transfer service, nor to the use of caboose cars now owned
by any railroad or railway company operating in this State.
At that time, there were 152 railroads (including subsidiaries and leased roads) operating in Illinois.
The report includes the legislation from Illinois, Iowa, Minnesota, Missouri, Montana, Nebraska, South Dakota, Wisconsin, Indiana, Arkansas, Maine, Michigan, New York, North Dakota, Ohio, Virginia, New Hampshire and Washington.