Jeffco or JeffCo may refer to:

• Jefferson County, Colorado
• Jefferson County, Missouri transit (JeffCo Express)
• Jefferson College (disambiguation), multiple schools

• 1939–40 Gauliga Ostmark
• 1939–40 Greek Cup
• 1939–40 Hong Kong First Division League
• 1939–40 Huddersfield Town A.F.C. season
• 1939–40 in Belgian football
• 1939–40 Indiana Hoosiers men's basketball team
• 1939–40 Irish League
• 1939–40 La Liga
• 1939–40 Latvian Higher League
• 1939–40 League of Ireland
• 1939–40 League of Norway
• 1939–40 Luxembourg National Division
• 1939–40 Maltese Premier League
• 1939–40 Manchester United F.C. season
• 1939–40 Montreal Canadiens season
• 1939–40 Nationalliga
• 1939–40 Nemzeti Bajnoksag I
• 1939–40 Nemzeti Bajnokság I
• 1939–40 Netherlands Football League Championship
• 1939–40 Newport County A.F.C. season
• 1939–40 New York Americans season
• 1939–40 New York Rangers season
• 1939–40 Národní liga
• 1939–40 OHA season
• 1939–40 Oldham Athletic A.F.C. season