In 1915 the southern part of Palm Beach County became Broward County . In 1917 the northwest part of the county became Okeechobee County . The southernmost part of Palm Beach County was separated to create the northern portion of Broward County in 1915 , the northwestern portion became part of Okeechobee County 1917 and southern Martin County was created from northernmost Palm Beach County in 1925 .