Warren is a city in Macomb County in the U.S. state of Michigan. The 2020 Census places the city's population at 139,387, making Warren the largest city in Macomb County, the third largest city in Michigan, and Metro Detroit's largest suburb.The city is home to a wide variety of businesses, including General Motors Technical Center, the United States Army Detroit Arsenal, home of the United States Army TACOM Life Cycle Management Command and the Tank Automotive Research, Development and Engineering Center (TARDEC), the headquarters of Big Boy Restaurants International, and Asset Acceptance. The current mayor is James R. Fouts, who was elected to his first mayoral term in November 2007.