Answer:
Yea, they are the same.
Although the words are used interchangeably there is a technical difference:
"Of" is a preposition used to denote place or direction, e.g., The Kingdom "of" Heaven is located in a place called Heaven; "of" is also used to denote ownership, e.g, The Kingdom "of" God belongs to God. The technical difference between the two is that the "Kingdom of God" encompasses and includes all rightful citizens of His Kingdom, whether now in Heaven, or whether still physically alive on this earth.