For many years before and after the establishment of Racine, he was a captain in the United States Revenue Cutter Service, commanding several ships in the Great Lakes.

As a young man, Gilbert Knapp studied the science of navigation, and, at age 13, joined the crew Captain Childs, his uncle by marriage, sailing to Canada and Spain.

[3][4] At the outbreak of the War of 1812, he joined the crew of the Leo, a privateer commanded by Captain Besonne, under contract to the United States to run dispatches to France.

In 1818, he joined the United States Revenue Cutter Service and sailed the great lakes, studying its harbors and tributary rivers.

During one of his many cruises on Lake Michigan, Captain Knapp went ashore at the mouth of the Root River to explore the region.

[1] The 1833 Treaty of Chicago, signed after the Black Hawk War, opened up the possibility for settlement on the west coast of Lake Michigan.

The treaty did not come into force until 1835, thus the land still belonged to the Potawatomi, but Knapp determined to settle the area before some other claim could be established.

[3] He sold his New York property and traveled to Chicago, where he obtained the investment of Gurdon Saltonstall Hubbard, an early settler in that area.

He camped in the area for two days, scouting the shore and river, and confirmed his earlier beliefs that the site would be appropriate for a settlement.

Barker purchased a one-third stake in the venture for $1,200 (about $35,000 adjusted for inflation to 2020), formally offered in a March 30, 1835, letter.

Thus Knapp, Hubbard, and Barker became equal financial partners in a claim of 140.98 acres on either side of the mouth of the Root River.

Later in 1835, Knapp brought his children from New York, and his sister, Sarah Milligan, became the first woman to join the town, bringing her three daughters as well.

At the time of the settlement at Port Gilbert, all of the present state of Wisconsin was part of the Michigan Territory.

[3] After the death of his third wife, Knapp lived the last decade of his life at the home of his daughter, Mary Annan McClurg, at the present site of the Racine Legacy Museum and Veterans Center, at 820 Main Street.

Honorary pallbearers included United States Senator James Rood Doolittle and Case Corporation founder J. I.