The Golf Course Superintendents of America group estimates that there are 2,244,512 acres of golf courses in the U.S. That area is about 3,507 square miles of land. Rhode Island is 1,040 square miles and Delaware is 1,950 square miles. You could almost put two Rhode Islands and a Delaware within the land space of all the golf courses in the U.S.

The estimated number of golf courses in the US is about 18,000. There is growing concern over the environmental impact of the course. For one, it consumes a LOT of water. The United Nations estimates that golf courses consume about 2.5 Billion gallons of water per day. They also use pesticides and fertilizers. There have been efforts to reduce the usage both of water, and of harmful substances. 

They're also getting larger. Because of new technologies that allow people to hit balls farther and farther, courses that used to be huge at 7,500-yards, are not rare anymore. 
(Sources 1, and 2)