v3.25.0.1
Cover - USD ($)
 12 Months Ended
Dec. 31, 2024
Mar. 31, 2025
Cover [Abstract]    
Entity Registrant Name MILL CITY VENTURES III, LTD.  
Entity Central Index Key 0001425355  
Document Type 10-K  
Amendment Flag false  
Entity Voluntary Filers No  
Current Fiscal Year End Date --12-31  
Entity Well Known Seasoned Issuer No  
Entity Small Business true  
Entity Shell Company false  
Entity Emerging Growth Company false  
Entity Current Reporting Status Yes  
Document Period End Date Dec. 31, 2024  
Entity Filer Category Non-accelerated Filer  
Document Fiscal Period Focus FY  
Document Fiscal Year Focus 2024  
Entity Common Stock Shares Outstanding   6,385,255
Entity Public Float $ 3,499,000  
Document Annual Report true  
Document Transition Report false  
Document Fin Stmt Error Correction Flag false  
Entity File Number 001-41472  
Entity Incorporation State Country Code MN  
Entity Tax Identification Number 90-0316651  
Entity Address Address Line 1 1907 Wayzata Blvd #205  
Entity Address City Or Town Wayzata  
Entity Address State Or Province MN  
Entity Address Postal Zip Code 55391  
City Area Code 952  
Icfr Auditor Attestation Flag false  
Auditor Name Boulay PLLP  
Auditor Location Minneapolis, Minnesota  
Auditor Firm Id 542  
Local Phone Number 479-1923  
Security 12b Title Common stock, $0.001 par value per share  
Entity Interactive Data Current Yes