His father, Peter Frelinghuysen Jr., served as the U.S. Representative from New Jersey's 5th congressional district from 1953 to 1975, representing much of the same area Rodney did during his time in Congress. On his father's side, he is a great-grandson of American Sugar Refining Company founder Henry Osborne Havemeyer and great-great-great-grandson of Ballantine Brewery founder Peter Ballantine. On his mother's side, he is a great-great-grandson of William Procter, co-founder of Procter & Gamble and grandson of William Cooper Procter, the president of Procter & Gamble from 1907 to 1930.