It is native to the central Salish Sea region in southwestern British Columbia and northwestern Washington, where it is an endemic species and is abundant on coast bluffs as well as on dry mountain ridges on the Olympic Peninsula.

[1] It was previously included in the description of the Rocky Mountain juniper (Juniperus scopulorum) but was separated in 2007.

[2] Genetic analysis revealed that what appeared to be Rocky Mountain junipers in the Puget Sound were not of the same species as those elsewhere.

The seaside juniper occurs at the edge of the water, next to the sound or the nearby lakes, in a milder, wetter climate on sandy, granite soils, even sand dunes in one location.

[2] In general the seaside juniper is common to abundant in its native range; however, it is impacted by development at some sites and it can face competition from Douglas-fir.