In the early days of the game (1870's-1880's)most home runs were inside the park, many ballparks didn't even have outfield fences and it's unlikely that inside the park homers were considered a separate stat from homers hit over a fence,a fairly rare occurence in the early days of the game.
babe ruth
the oldest major league baseball park is the Fenway park the home of the Boston Red Sox
Fenway Park is in Boston, home of the Red Sox
Ty Cobb of the Detroit Tigers lead the American League in home runs with 9 in 1909, all were "inside-the-park" homers.
90 Feet
Lou Gehrig hit his first major league home run on September 27, 1923. It was against the Boston Red Sox at Fenway Park.
it varies from ballpark to ball park there is no regulation
If your counting from 1876, when the National League started, Ross Barnes, second baseman for Chicago, was the 1st when he hit an inside the park home run in the 5th inning against William "Cherokee" Fisher if Cincinnati on May 2, 1876.
The oldest mlb stadium is fenway park in Boston home of the red sox
Fenway
fenway park
The oldest major league ball park is Fenway Park, home to the Boston Red Sox who first played there in 1912. Next is Wrigley Field home of the Chicago Cubs. Their first game at Wrigley was in 1914. The third oldest park jumps ahead 50+ years to 1962 and the Los Angeles Dodgers' Dodger Stadium.