Document and Entity Information - shares
 9 Months Ended
Sep. 30, 2020
Nov. 05, 2020
Document and Entity Information    
Entity Registrant Name Mid-Southern Bancorp, Inc.  
Entity Central Index Key 0001734875  
Trading Symbol msvb  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Title of 12(b) Security Common Stock, par value $.01 per share  
Entity Common Stock, Shares Outstanding   3,174,657
Document Type 10-Q  
Document Period End Date Sep. 30, 2020  
Amendment Flag false  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q3  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company false