| Document and Entity Information | Oct. 21, 2020 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Oct. 21, 2021 |
| Entity File Number | 001-40255 |
| Entity Registrant Name | WILLIAM PENN BANCORPORATION |
| Entity Incorporation, State or Country Code | MD |
| Entity Tax Identification Number | 85-3898797 |
| Entity Address State Or Province | PA |
| Entity Address, Address Line One | 10 Canal Street |
| Entity Address, Adress Line Two | Suite 104 |
| Entity Address, City or Town | Bristol |
| Entity Address, Postal Zip Code | 19007 |
| City Area Code | 267 |
| Local Phone Number | 540-8500 |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | WMPN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001828376 |
| Amendment Flag | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
