v3.23.1
Cover - USD ($)
 12 Months Ended
Dec. 31, 2022
Mar. 31, 2023
Jun. 30, 2022
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, 2022    
Entity Filer Category Non-accelerated Filer    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2022    
Entity Common Stock Shares Outstanding   6,185,255  
Entity Public Float     $ 5,625,200
Document Annual Report true    
Document Transition Report 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    
Entity Address Address Line 2 #205    
Entity Address City Or Town Wayzata    
Entity Address State Or Province MN    
Entity Address Postal Zip Code 55391    
City Area Code 952    
Local Phone Number 479-1923    
Entity Interactive Data Current Yes    
Icfr Auditor Attestation Flag false    
Auditor Name Boulay PLLP    
Auditor Location Minneapolis, Minnesota    
Security 12g Title Common stock, $0.001 par value per share    
Auditor Firm Id 542