Floods are natural disasters that cause loss of life and property destruction. The objective of this study was to analyze flood hazards and inundation area mapping of the Wabash River Basin. Flood-generating factors, i.e., slope, elevation, rainfall, drainage density, land use, and soil type, were rated and combined to delineate flood hazard zones for determining average water surface elevation for the downstream, average inundation width, and area for each simulation. This paper includes the steps to run the HEC-RAS model by describing each step for making an inundation map of a flooded area. The flooded areas along the Wabash River have been mapped for different profiles (2, 10, 50, and 100 years) return periods and by increasing and decreasing Manning’s coefficient by 10 and 20% using the HEC-RAS model. The major findings in the study revealed that inundated area and water surface elevation are insignificantly affected by changing values of Manning’s coefficient. There is high variation in water surface elevation and inundation area for different return periods, i.e., both decrease from a 100-year return period to 2-year return period.