The original 1891 hotel was a large three-story structure with projecting bays at each end. Its construction was supervised by R.R. Cummins for the Northern Pacific Railway, which was building two other, similar hotels in the park. Reamer's 1903 remodeling changed these projections to the present Ionic porticoes. An eastward extension was added at this time, with a third matching portico. In 1922-23 a further extension to the east was undertaken, this with a flat roof. In 1928 a two-story west wing was added, expanding the dining room and adding a solarium to the front. The entire hotel was extensively renovated from 1984 to 1990.
The west wing of the Lake Hotel was renovated in the winter and spring of 2012, including the formal dining room and beautiful sun room/lounge. The remaining rooms in the east end of the hotel will be renovated during the fall and winter of 2013-2014.