I studied in the US up until the 6th grade, came back to India, completed high school here and finished a bachelor degree in computer science here in India. All my education in India was completed in English only. I am also a US citizen. I want to pursue a masters degree in the US. Do I need to take the TOEFL exam or not?
The safest course of action would just be to take it.
Each department at each university has its own policy on the TOEFL. Usually international students from non-English speaking countries are required to take it, but there may be exceptions. It is common for there to be an exception for students who have attended a university in the US, but that does not apply to you.
So you'd have to check the policies of each department where you want to apply, to see if they have an exception that does apply to you. Or, if there is no written exception that applies, you could contact them directly, explain your situation, and ask them to waive the requirement (of course there is no guarantee that they will agree).
So unless you can verify that every department you care about will accept you without a TOEFL score, you had better take the exam.
Most schools will say that they don't require the TOEFL if the language of instruction in your previous institution was English.
In reality, if you're applying from outside USA/England/Australia/New Zealand, then it's a very good idea to have TOEFLs (unless your GRE verbal scores are very high - top 10 percentile).
You want to extinguish any possible doubt about your English-speaking ability.