Our nation's 28^th President, Woodrow Wilson, is entombed on the main floor of the Cathedral Church of St. Peter and St. Paul, better known as Washington National Cathedral, in Washington, D.C.  According to the National Cathedral website, Woodrow Wilson is the only U.S. President buried within the boundaries of the District of Columbia. 

President George Washington is buried in Virginia on the grounds of his beloved Mount Vernon; President Kennedy lies at the JFK Memorial in Arlington National Cemetery in Arlington, Virginia; and Ulysses S. Grant is entombed at the General Grant National Memorial in Riverside Park in New York City.

Bonus Question:

Why are the Nation's 22^nd and 24^th Presidents buried in the same place?

Answer:

Grover Cleveland was elected to the office of President twice, but not consecutively.  He was defeated in 1889 by Benjamin Harrison, who served as President for 4 years.  Cleveland was re-elected in 1893, therefore serving as the 22^nd and 24^th President of the United States.

He is buried in Princeton, New Jersey.