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The Plaza Inn is significant as the sole remaining hotel/apartment building left in Hot Springs State Park. It represents the beginning of commercialization in the State Park which started in the early 1900s. At one time there were over six facilities to provide the sick and ailing access to the healing waters of the Big Spring, the most famous being the Carter Hotel and Sanitarium which was demolished in 1966. James McLaughlin, United States Indian Inspector, reported to the Department of the Interior in 1896, his findings and opinions on what is now known as the Hot Spring State Park. ''The water of this spring is said to possess wonderful curative properties and to be very beneficial for rheumatic and other ailments, and although the temperature is 132 degrees it is not unpleasant to drink, and with salt and pepper added tastes very much like fresh chicken broth.'' (Senate Document No. 247, 54th Congress, 1st Session.) The park was purchased by the government from the Shoshone and Arapahoe Indians in 1897, and the Hot Spring State Reserve was formed.

The commercial development of Hot Springs State Park Reserve began soon after a small settlement located at the mouth of the Owl Creek moved to the Hot Springs. Thermopolis (Greek meaning ''Hot City'') sprang to life with tourist activity when a series of hotels were constructed in the new state park. The last hotel was built by brick layer James Callaghan beginning in November 1917. By June of 1918 the Callaghan Apartments were ready for guests. Mr. Callaghan and his wife Hazel ran the hotel a short time. The two story brick structure originally housed 70 rentable rooms, divided into fourteen sections, each hall containing a common bathing room at the end of each corridor. In 1921 Dr. P. W. Metz purchased shares in the Callaghan Apartment Company, Inc. and ownership was legally transferred. Dr. Metz renamed the hotel Plaza Apartments and Hotel and it has been referred to as the Plaza since then. Ownership has changed many times, but the business at hand has always been to provide guests of the Plaza access to the mineral baths.