The city is on Sanibel Island on the Gulf coast of Florida and is linked to the mainland by a toll causeway which runs across two small islets. A further short causeway links Sanibel Island to Captiva Island. The beaches are excellent on both islands. Sanibel Island is home to a good variety of birds, including Magnificent frigatebird.
Birds can be seen on the beaches, the causeway islands and the reserves, including J Ding Darling. The rare American crocodile has been be seen at the latter site.
According to the United States Census Bureau, the city has a total area of 85.9 km² (33.2 mi²). 44.6 km² (17.2 mi²) of it is land and 41.3 km² (16.0 mi²) of it is water. The total area is 48.13% water.
As of the census of 2000, there are 6,064 people, 3,049 households, and 2,125 families residing in the city. The population density is 136.0/km² (352.4/mi²). There are 7,075 housing units at an average density of 158.7/km² (411.2/mi²). The racial makeup of the city is 97.99% White, 0.94% African American, 0.08% Native American, 0.33% Asian, 0.05% Pacific Islander, 0.12% from other races, and 0.49% from two or more races. 1.39% of the population are Hispanic or Latino of any race.
There are 3,049 households out of which 10.7% have children under the age of 18 living with them, 65.3% are married couples living together, 3.2% have a female householder with no husband present, and 30.3% are non-families. 25.9% of all households are made up of individuals and 14.7% have someone living alone who is 65 years of age or older. The average household size is 1.99 and the average family size is 2.33.
In the city the population is spread out with 10.1% under the age of 18, 1.7% from 18 to 24, 12.4% from 25 to 44, 35.8% from 45 to 64, and 40.0% who are 65 years of age or older. The median age is 60 years. For every 100 females there are 90.6 males. For every 100 females age 18 and over, there are 88.9 males.
The median income for a household in the city is $79,044, and the median income for a family is $92,455. Males have a median income of $40,641 versus $27,481 for females. The per capita income for the city is $66,912. 3.2% of the population and 2.0% of families are below the poverty line. Out of the total people living in poverty, 2.8% are under the age of 18 and 1.5% are 65 or older.