After entering the Fukuyama Domain, Katsunari hired the highly-respected and resourceful Chikanari MIMURA who was his benefactor during his wandering years as a position of chief retainers by giving him a high salary to carry out domain duties, and he engaged actively in castle town construction, promotion of industrial development, embankment works, and development of new rice fields, and laid the foundation for the present-day Fukuyama City area which was mostly a wetland before.
福山入封後は放浪時代の恩人で知謀の名高い三村親成を高禄で家老職に迎え藩政に力を注ぎ、城下町の建設、産業育成、治水工事や新田開発を積極的に行い、それまでは概ね湿地帯であった現在の福山市域の発展の礎を築いた。