Not much is known of his work for the next 20 years. He exhibited landscape paintings at various showings sponsored by the Pennsylvania Academy of Arts in Philadelphia, and engraved at least three pictures by William Birch (1801, 1803, 1804).

In early 1819, Seymour accompanied the Major Stephen H. Long Expedition as landscape painter. The following year, the exploration went to the Platte River, the Front Wall of the Rockies, and down the Arkansas/Canadian Rivers. On the return trip, the party stopped for ten days in September at Fort Smith, a log frontier outpost located at the junction of the Arkansas and Poteau Rivers on the western border of the Arkansas Territory. While there, Seymour made at least two, possibly three, drawings of the fort and its environs. Then, Seymour, in company with Peale and Say, returned to Philadelphia, via New Orleans, arriving there in late December, 1820.

During the next two years, Seymour reportedly finished some 60 of the 150 sketches he made while on the exploration trip. Of all this work, however, only 17 of his drawings from the 1819-1820 expedition can be identified today.

In 1823, Seymour again accompanied Long on an expedition, this time to the headwaters of the St. Peter's River in Minnesota. Returning from this trek by October 26 of that same year, the artist again provided a number of drawings for the official report of the exploration party, presumably finishing these by mid-1824. From this point on, Samuel Seymour disappears from historical sight. (Clyde Dollar, Research Brief: The Artist, Samuel Seymour, at Fort Smith, 1820. June 10, 1975.)

from:  Academy of Natural Sciences of Philadelphia