OK -- this may sound like circular logic, but remember this is Disney.
Reedy Creek Improvement District is an independent government entity created by Lake Buena Vista and its sister city Bay Lake. LBV has about 40 citizens and Disney owns virtually all its land.
Reedy Creek Improvement District isn't necessarily owned by WDW -- a company can't really own a government. WDW (and some other property owners) pays taxes to RCID -- which then provides services to WDW by contracting with wholly owned subsidiaries of WDW Co., such as Reedy Creek Energy Services, Reedy Creek Pest Control, Reedy Creek Fire Services and any other manifestation of the Reedy Creek name you might wish to develop.
The RCID government can regulate land use, provide police and fire services, license the manufacture and sale of alcoholic beverages, build roads, lay sewer lines, construct waste-treatment plants, carry out flood projects and even build an airport -- all without local or state approval.