Visitors to Lilly House begin their first-floor tour of the home in the Stair Hall. The original design of the house, which was built for the Landon family, had the mansion's main entrance opening into this room, which featured a square staircase. The Lillys replaced the Landon's square staircase with a circular one and moved the home's main entrance to a more central location that opens into the Great Hall.

The Great Hall is the largest room in Lilly House and it provides access to most of the other rooms on the first floor. The Great Hall served as the main room for entertaining. The mansion's main entrance opened into this room after the Lilly's initial remodeling of the home in the 1930s. Spacious and formal, the Great Hall corresponds to the Allée, the grandest of Oldfields' landscape features.

Of all the rooms in Lilly House, the Game Room has undergone the most dramatic changes through the years. During the Landon's occupancy of the house, this room featured gothic-style oak woodwork and shoulder-high bookcases. In the 1930s, the Lillys covered the walls with birds-eye maple and installed floor-to-ceiling bookcases and a marble fireplace. During the redecorating project of the 1950s, the Lillys needed wall space to display a collection of paintings, so the bookcases were covered and the walls were painted.

By the time he purchased Oldfields in 1932, J.K. Lilly Jr. had been actively collecting rare books for about six years. He built a handsome, walnut-paneled library to house them by expanding what had been a sun room or enclosed porch at the southern end of Lilly House. This large but intimate Georgian-style library is the most remote and private room on the main level. French doors on the south wall open to an axial view along a path leading to the Formal Garden.

The Drawing Room was used by the Lillys as a smaller public room. Interior design in the early 20th century emphasized architectural elements, and the Lillys honored this by adding moldings to the walls to surround panels of hand-painted Chinese wallpaper. The room was furnished to carefully limit competing patterns, making the wallpaper the dominant design feature. A reproducing piano (a technically advanced type of player piano popular in the early 1900s) was used here for musical entertainment. In the 1950s, the moldings were removed and the walls were covered with silk to accommodate a group of painted portraits.

Loggias were common features of country houses in the early 1900s, providing transitional spaces between the house and the outdoors. The Landons had used wicker and painted wood furniture in this room, while the Lillys gave the room a more finished treatment in their 1930s-era remodeling. In the 1950s, the Lillys commissioned Canadian muralist Douglas Riseborough to create landscape murals on the walls of the loggia. His paintings are fanciful interpretations of the view from the front of Lilly House. The loggia is the only room within Lilly House that has been restored to the 1950s period of the Lilly family's occupancy. The rest of the rooms have been restored to their appearance during the initial Lilly family remodeling of the early 1930s.

With its west-facing windows, the Lilly House dining room was well-positioned for evening sunlight. While the Landons lived in the home, the dining room walls were paneled with mahogany. In keeping with the fashion of the times, the Lillys brightened this room by covering sections of the mahogany paneling with muslin and painting the walls.

When the Lillys remodeled in the 1930s, they updated the kitchen with some new cabinets as well as new linoleum floors and countertops. The zinc edges of the countertops are consistent with the architect's drawings for Lilly House. A refurbished six-burner Magic Chef stove has been positioned in this area. At the kitchen's north end is a small room that contained a refrigerator, a service porch for deliveries and a sitting room for employees. Adjacent to the kitchen is the Butler's Pantry, which served as a buffer between the kitchen and dining room. Here food could be prepared for serving, and fine tablewares could be washed and stored in the cabinets and drawers.

The second floor of Lilly House features educational and interactive exhibits that allow visitors to explore subjects including architecture, interior design, landscape architecture, the history of Oldfields and the American Country Place era and the history of the Lilly family and Eli Lilly & Company. Samples of Mr. Lilly's extraordinary collections of books, gold coins, military miniatures and nautical items are also on display.