Grand Bay is a census-designated place (CDP) in Mobile County, Alabama, United States. It is included in the Mobile metropolitan statistical area. The population was 3,672 at the 2010 census.
Grand Bay is located at 30°28′27″N 88°20′31″W (30.474055, -88.341836), along U.S. Route 90 midway between the Alabama/Mississippi state line and the town of St. Elmo, a few miles inland from the Mississippi Sound.
According to the United States Census Bureau, the CDP has a total area of 8.7 square miles (23 km2), of which 8.7 square miles (23 km2) is land and 0.04 square miles (0.10 km2) (0.34%) is water.
As of the census of 2000, there were 3,918 people, 1,364 households, and 1,078 families residing in the CDP. The population density was 452.3 people per square mile (174.7/km2). There were 1,441 housing units at an average density of 166.4 per square mile (64.2/km2). The racial makeup of the CDP was 89.00% White, 8.88% Black or African American, 0.23% Native American, 0.79% Asian, 0.05% Pacific Islander, 0.13% from other races, and 0.92% from two or more races. Hispanic or Latino of any race were 0.87% of the population.
There were 1,364 households, out of which 37.5% had children under the age of 18 living with them, 65.5% were married couples living together, 10.0% had a female householder with no husband present, and 20.9% were non-families.