Joel Barlow High School is a public high school serving students in ninth through twelfth grades in Redding, Fairfield County, Connecticut, United States. The school serves Easton and Redding students.

The school is the sole institution in the Region 9 School District of Connecticut, made up of the towns of Redding and Easton, which each have their own public school systems for education up to the eighth grade. The Board of Education acts as its own Board of Finance, and although it reports to the boards of finance in both towns, they have no control over the school budget. Each year a referendum is held on the school budget and must be passed by a majority of voters in the two towns.

As of the 2015-16 school year, the school had an enrollment of 1,008 students and 71.4 classroom teachers (on an FTE basis), for a student–teacher ratio of 14.1:1. There were 33 students (3.3% of enrollment) eligible for free lunch and 12 (1.2% of students) eligible for reduced-cost lunch.

For the purpose of comparison with the achievement levels of similar schools, the state Department of Education classifies schools and communities in "District Reference Groups", defined as "districts whose students' families are similar in education, income, occupation and need, and that have roughly similar enrollment". Its total minority enrollment is 13%, 6% of which are Hispanic. Joel Barlow High School (Region 9) is one of eight school districts in District Reference Group A (others are Darien, Easton, New Canaan, Redding, Ridgefield, Westport, and Wilton). It is ranked #15 within the state of Connecticut and #696 in National Rankings of Public High Schools.