Population growth continued at a brisk pace in Montgomery and Bucks Counties over the last decade, according to official U.S. Census figures released Wednesday. Montgomery County grew by 6.6 percent, gaining 49,777 residents and raising the total figure to 799,874. Bucks County grew by 4.6 percent, gaining 27,614 residents to a total figure of 625,249. The counties remain the third and fourth most populous in Pennsylvania. The state population grew by 3.4 percent, to 12,702,379, and it remains the sixth most populous state. The growth was mostly in the southeast and the Poconos. Philadelphia’s population grew slightly over the last decade, reversing a decline that started in the 1950’s. Census figures show a growth of more than 8,000 people, or about six tenths of one percent, to a total of about 1,526,000. Its population peak in the 1950 census was a little more than two million.