Ingham County has a total area of 1,453 km˛ (561 mi˛). 1,448 km˛ (559 mi˛) of it is land and 5 km˛ (2 mi˛) of it is water. The total area is 0.31% water. The county consists of gently rolling hills with an elevation ranging between 800 to 1000 feet above sea level. According to the U.S. Census Bureau in 2000, there are 279,320 people, 108,593 households, and 63,744 families residing in the county. The population density is 193/km˛ (500/mi˛). There are 115,056 housing units at an average density of 79/km˛ (206/mi˛). The racial makeup of the county is 79.46% White, 10.86% Black or African American, 0.55% Native American, 3.68% Asian, 0.05% Pacific Islander, 2.42% from other races, and 2.99% from two or more races. 5.80% of the population are Hispanic or Latino of any race.

There are 108,593 households out of which 29.80% have children under the age of 18 living with them, 43.00% are married couples living together, 12.10% have a female householder with no husband present, and 41.30% are non-families. 30.20% of all households are made up of individuals and 7.70% have someone living alone who is 65 years of age or older. The average household size is 2.42 and the average family size is 3.04.

The median income for a household in the county is $40,774, and the median income for a family is $53,063. Males have a median income of $40,335 versus $30,178 for females. The per capita income for the county is $21,079. 14.60% of the population and 8.30% of families are below the poverty line. Out of the total population, 14.60% of those under the age of 18 and 6.60% of those 65 and older are living below the poverty line. The county seat is Mason.

Neighboring areas include: Shiawassee County, Livingston County, Washtenaw County,Jackson County, Eaton County, and Clinton County.