Not just in Ferguson, Missouri, in total there are presently 30 different states of emergency in US

A proclamation by governor Jay Nixon authorizes the Missouri National Guard to support police if there is violence when a grand jury decision is announced on whether a white policeman who shot and killed an unarmed black teenager will be charged.

The exact proclamation can be found here. Governor Nixon said: "As part of our ongoing efforts to plan and be prepared for any contingency, it is necessary to have these resources in place in advance of any announcement of the grand jury’s decision." The order also designates the St. Louis Police Department rather than the Ferguson police to be in charge of policing any protests that might arise as a result of the decision. There have already been protests in Clayton, Missouri, where the grand jury is meeting. The decision is expected some time in November. The state of emergency was for thirty days but can always be extended.
Many states of emergency are extended for years. In 1979 on the 10th day of the Iranian hostage crisis, then president Jimmy Carter declared a state of emergency. It is still in effect about 35 years later. The post 9/11 state of national emergency issued by president George W. Bush has been renewed six times by Obama. He uses the state of emergency for many of his actions in the war on terror. States of emergency are very convenient for giving officials extra-ordinary power. In the US at present there are a total of thirty distinct states of emergency in effect.
 Some states of emergency seem only marginally related to any significant immediate threat to the United States. For example, recently Obama informed the US Congress that he was extending a state of emergency with respect to the Democratic Republic of the Congo that had been passed in the Bush era because the "widespread violence and atrocities" in that country "pose an unusual and extraordinary threat to the foreign policy of the United States".
 Emergency declarations allow the president extraordinary powers to seize property, call up the National Guard, and also hire and fire military officers as he wishes. Kim Scheppel of Princeton University said:"What the National Emergencies Act does is like a toggle switch, and when the president flips it, he gets new powers. It's like a magic wand. and there are very few constraints about how he turns it on," Since the National Emergencies Act was passed in 1976 presidents have declared 53 states of emergency but this does not count declarations during natural disasters such as hurricanes or floods. Since Obama has been in office he has declared nine emergencies but also extended 22 others that were already in effect. Only one declaration has been allowed to expire.The 1976 law requires both houses of Congress to meet within six months of a declaration to vote it up or down. Apparently this has never happened.
Attorney Patrick Thronson in a University of Michingan law journal identified 160 different laws giving presidents broad unchecked powers. These include the power to: • Suspend environmental laws, including a law forbidding the dumping of toxic and infectious medical waste at sea.• Bypass federal contracting laws, allowing the government to buy and sell property without competitive bidding.
  Harold Relyea of the Congressional Research Service said: "The history here is so clear. The Congress hasn't done much of anything. Congress has not been the watchdog. It's very toothless, and the partisanship hasn't particularly helped." Scheppele claims that declarations of emergencies have now become so routine they often do not even generate a single headline:"If we had to break the glass and flip the switch in order to do it ... it would be helpful for the alarm to go off at least. It's a sign that normal law isn't set up right. States of emergency always bypass something else. So what we need to look at is what's being bypassed, and should that be fixed."