Courtney Adcock, 36, and Steve Adcock, 39, retired in their mid-30s with a combined net worth of $870,000. This FIRE couple lives off the grid in the Arizona desert and spends $40,000 a year.

This is an installment of CNBC Make It's Millennial Money series, which profiles people around the world and details how they earn, spend and save their money.

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