Jefferson Street Grounds was a baseball field located in Philadelphia, Pennsylvania. It was also known as Jefferson Park and Athletics Park. It was home to three different professional baseball teams, competing in three different leagues. Notably, it was the venue for the first game in National League history, played on April 22, 1876.

The grounds were located on a large block bounded by Jefferson Street (north); 25th Street (east); Master Street (south); and 27th Street (west). Across the street to the south was the Spring Garden Reservoir, which has since been filled in. Although typically listed as one ballpark, the 1870s diamond was located in the opposite corner of the block from the 1880s diamond. The facility opened to professional league baseball during 1871, as early as May 15. The club's first official National Association home game was played on June 3. The seating capacity was meager, only 5,000 seats. The inaugural National League game was played there, on Saturday, April 22, 1876, between Athletic and Boston; the Bostons won, 6–5. By a quirk of fate, it was the only National League game played that day, all others being rained out. This game is often pointed to as the beginning of Major League Baseball.

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