This depends on your residential area zoning laws.
Some zones limit homes to one per 3 acres, or even 10 acres.
In some locations like New York City, you can have 4 or more town houses per acre and they can be high rise.
In most non megopolises, you will find one home per quarter acre.
Some cities will divide up the acreage into lots, and then desigante a certain number of lot on which to build. IN Browns Mills, NJ for example, 3 lots are required to build. That would put about 5 or 6 homes per acre.
Check your zoning laws.