He gained more territories as a reward for the Battle of Dewa in the Keicho era, which was associated with the Battle of Sekigahara, gained the current whole Yamagata Prefecture and Yurihonjo City, Akita Prefecture (which were replaced by Ogachi County and Hiraka County by agreement with the Satake clan in 1602), became Daidaimyo (a feudal lord having a greater stipend) with a total fief of 570,000 koku (the actual yield was considered 1,000,000 koku) and reached the high watermark again.
関ヶ原の戦いに伴う出羽合戦の恩賞で加増され、置賜郡を除く現在の山形県全土と秋田県由利本荘市周辺（1602年、佐竹氏との領土交換により雄勝郡・平鹿郡と引き換えた）を手に入れ、計57万石（実高は100万石とも称する）を領する大大名になり、二度目の最盛期を迎える。