Mountain lions (Puma concolor) have many impacts on the ecosystems they inhabit, leading to both biological and social ramifications. Yet, due to the relatively recent natural recolonization by mountain lions of the Little Missouri Badlands Region of western North Dakota, detailed data regarding many aspects of this population have been lacking. We studied mountain lions occupying the Badlands Region to improve our understanding of the characteristics of the North Dakota mountain lion population. Our objectives included estimating annual survival rates, documenting sources of mortality in this population, and creating a population model using statistical population reconstruction (SPR) techniques. Between 2012 and 2016, the average annual survival rate estimated from known fate models was 0.456. Sex-specific annual survival was estimated at 0.589 for females and 0.259 for males. We recorded 17 cause-specific mortalities of marked mountain lions over the same 5 y period, plus the probable failures of two litters of marked dependent kittens. Results from our population model indicate annual population abundance estimates between 2005 and 2017 ranged from a low of 27 total mountain lions in 2005–2006 to a high of 165 in 2011–2012. The model indicated an increasing trend in total abundance between 2005 and 2012, then a reversal and sharp drop in abundance from 2012 to 2014, until the trend leveled with similar total abundances from 2014 to 2017. The results from our study can help inform current and future management decisions in North Dakota and may also provide insight for managers faced with potential mountain lion recolonization further eastward in the United States.