The primary habitat of the Garden Dormouse is woodland (coniferous, deciduous, and mixed) areas from the sea level up to the tree line and beyond. The species could also be found in rocky areas far from trees and in orchards, gardens, quarries, and abandoned scrub. It is less arboreal than other dormice and is often found on the ground in rocky areas, cracks in stone walls, hives and even in houses (Palomo and Gisbert 2002, Spitzenberger 2002, Bertolino 2007). In Germany, it also occurs in urban areas, including cities (Nava et al. 2022). This species could adopt communal and singular nesting reproductive strategies (Viñals et al. 2017). The generational length is approximately two years (Amori et al. 2016). The species is more carnivorous than other dormice and seems to depend on arthropods as food (Büchner et al. 2022b).

The Garden Dormouse (Eliomys quercinus) is endemic to Europe, where it historically occurred from Portugal to the Urals (Russia) and from Finland to southern Italy. It is now primarily confined to western Europe, with only scattered populations in the east. Its altitudinal range is from sea level to 2,000 m.

The species is considered extinct in Lithuania, Finland, and Slovakia (Juškaitis 2003, Bertolino 2017), probably in Belarus (the last two records in 1962 and 1996, Bertolino 2017), Latvia (no records since the mid-1990s, despite widespread monitoring, Pilāts 2022), Estonia (last record in 1986, Timm and Maran 2020), and present with single populations in the Netherlands, Poland (the last certain record in 1960s from Zawoja, vicinity of Babia Gòra, Cichocki et al. 2022), and Slovenia (only one record, Kryštufek 2003). The species is rare and localised in Austria (Spitzenberger 2002) and Croatia and is in regression in Germany (Meinig and Büchner 2012), Flanders (Belgium), and Czechia (Andera 1994). Museum and literature records from Romania (Hegyeli 2022) and Ukraine (Misthta 2022) are questionable. Old records of alleged Garden Dormouse in Romania were misinterpreted, and presently, there are no museum specimens nor publications with photos, measurements or detailed descriptions of individuals confirming the present or past presence of the species in the country (Hgyeli 2022). Most of the specimens in the Ukrainian museums were attributed to the Forest Dormouse (Dryomys nitedula), and the only specimen of E. quercinus collected in 1965 was assigned to a non-existent settlement (Mistha 2022).

Its range contracted by 33% between 2008 and 2015 (Bertolino 2017) following on from a >50% decline in the 30 years previously (Meinig and Buechner 2012). The distribution of the Garden Dormouse was reviewed by Bertolino (2017). The species is introduced in the UK.

The species is listed on Appendix III of the Bern Convention. There is a need to determine why the populations in the central-eastern part of the range are in decline, to monitor them, and to identify and implement appropriate conservation measures. The species is assessed as Regionally Extinct in Estonia, Latvia and Lithuania, as Critically Endangered in Czechia, Poland and Ukraine, Endangered in Flanders and Germany, and Near Threatened in Austria, Italy, Portugal and Spain.