Hanes Ifan Cyffredin Glas, 1795. An unpublished work in which William Wililams expresses his opinion on the state of religion and society. (Original and copy)
A volume of herbal recipes and remedies, 1803.
Dadl rhwng Tudur a Gronwy ar Etholedigaeth ac Ymneillduaeth (A debate between Tudur and Gronwy on election and dissent)
General view of the agriculture of North Wales, 1794 by George Kay with holograph notes and observations by William Williams.