What team is the oldest in the MLB?

Answer 1

the Atlanta Braves are the oldest franchise still in operation

The Cinci Reds are the oldest professional ballclub

The Braves and the Cubs both started in 1876. The Reds aren't the same Reds that play today. The current team, along with the Pirates, came into being in 1882.

Answer 2

The National League team playing in Chicago has a continuous history since 1876, although they have changed their nickname. The team now known as the Braves has also existed since then, although they have changed their name and their city more than once. The NL team playing in Philadelphia has had the name "Phillies" continuously since 1883.

Prior to 1876, no Baseball team was part of a LEAGUE of CLUBS with a set schedule or player contracts that applied between organizations. The National Association of Baseball PLAYERS existed from 1871 to 1875, but its teams had schedules and contracts that can charitably be described as "haphazard."