My US refund shows in my checking account but now a good amount of it has been withdrawn. I don't understand?

Is the amount sent/issued by the IRS the same as the refund amount shown on your federal tax return Form 1040 Line 35a? - https://www.irs.gov/refunds

If not, then go to this IRS website for information on reduced refunds - https://www.irs.gov/taxtopics/tc203

Are you also receiving a state tax refund?  The state tax refund is separate from the federal tax refund.
Use this TurboTax support FAQ to check the state tax refund status - https://ttlc.intuit.com/questions/1899433-how-do-i-track-my-state-refund