[1] Found in northern Europe and northeastern North America, it grows on siliceous rocks, often between mosses, typically on rain-sheltered damp surfaces.

The holotype specimen was collected by Orange on 25 January 2005 in Merioneth, Wales (VC 48), near Rhyd-y-sarn, at an elevation of 90 m (300 ft).

[3] Lepraria humida is found in Great Britain, with confirmed records from Wales, northwest England, and Scotland, supported by internal transcribed spacer sequencing.

The distribution of Lepraria humida is likely underestimated, as it is often overlooked in the field or mistaken for more common species within the widespread L. neglecta group.

[5] It frequently occurs alongside other lichens, including Cystocoleus ebeneus, Lepraria bergensis, L. incana, L. membranacea, Micarea botryoides, Opegrapha gyrocarpa, and Psilolechia lucida, as well as bryophytes such as Cynodontium bruntonii, Dicranum scoparium, Diphyscium foliosum, and Diplophyllum albicans.