Haslett is a census-designated place (CDP) in Ingham County in the U.S. state of Michigan. It is located mostly within Meridian Charter Township with a small portion extending east into Williamstown Township. The population was 19,220 at the 2010 census. Haslett contains its own school district, as well as its own post office with the 48840 ZIP Code.

Ingham County is a county located in the U.S. state of Michigan. As of the 2020 Census, the population was 284,900. The county seat is Mason. Lansing, the state capital of Michigan, is largely located within the county. Lansing is the only state capital in the United States located in a county of which it is not also the seat of government. The county is home to Michigan State University, Lansing Community College, and the Class A minor league baseball team Lansing Lugnuts. Ingham County is included in the Lansing–East Lansing, MI Metropolitan Statistical Area. It is considered to be a part of Mid Michigan.