Allt Derlwyn (Topographic feature).
Grid Reference: SN 45371 30464. Parish: Llanllawddog, Carmarthenshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Bryn Derlwyn (Unclassified).
Grid Reference: SN 95320 99421. Parish: Carno, Montgomeryshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Careg y Derlwyn (Unclassified).
Grid Reference: SN 80699 70926. Parish: Ysbyty Ystwyth, Cardiganshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Cefn Derlwyn (Unclassified).
Grid Reference: SN 92694 47512. Parish: Treflys, Brecknockshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Coedcae y Derlwyn (Unclassified).
Grid Reference: SN 88441 01344. Parish: Glyncorrwg, Glamorgan
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Craig Derlwyn (Unclassified).
Grid Reference: SN 72058 15638. Parish: Quarter Bach, Carmarthenshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Craig y Derlwyn (Unclassified).
Grid Reference: SH 69992 25567. Parish: Llanddwywe-uwch-y-graig, Merionethshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Cwm-Derlwyn Wood (Unclassified).
Grid Reference: SN 87269 07313. Parish: Neath Higher, Glamorgan
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Derlwyn (Settlement).
Grid Reference: SN 44458 30668. Parish: Llanllawddog, Carmarthenshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website

Derlwyn (Unclassified).
Grid Reference: SN 66321 60380. Parish: Caron-is-clawdd, Cardiganshire
When recorded: 1898-1908. Primary Source: OS 2nd Edition Maps. Secondary Source: GB1900 website