In January 2018, The Colorado Futures Center, in partnership with Shift Research Lab, released Exploring Colorado’s Housing Affordability Challenges, which revealed a largely unexplored phenomenon: more Coloradans are living with friends, roommates and family members in “doubled-up” households. This brief, the first in a two-part series, explores the data on doubled-up households in Colorado, describing the demographics, geographic distribution and change in the prevalence of the doubling-up phenomenon from 2006 to 2017. The second part in the series, which will be released later this year, will explore the economic circumstances surrounding these households, with a specific focus on the impact of the COVID-19 crisis.