Jean-Dominique, comte de Cassini (1748 – 1845) was a French astronomer.
Cassini was born to a family of astronomers at the Paris Observatory on 30 June 1748. He entered the French Academy of Sciences in 1770, and gradually took his father's place as director of the observatory.
Following the outbreak of the French Revolution, Cassini was commissioned to create a new measurement system, and set about devising the metric system. He also participated in plotting a general map of France. Cassini's aristocratic origins brought him into conflict with the National Assembly, and the latter opposed his plans for the observatory.
In September 1793, he resigned from his position, and was imprisoned the following year. After seven months, he was released. Cassini planned to retire to his provincial Château de Thury with his wife. However, he had unintentionally left several celestial observations at the observatory. The Assassin Arno Dorian was able to retrieve the observations, and upon receiving them, Cassini explained that the observations confirmed several of his ideas. He and his wife then left Paris for their provincial château at Thury.