Fremont Township is a township in Lake County, Illinois, USA. As of the 2020 census, its population was 33,422. The land of the township was first settled by Europeans in 1835, and the first permanent settlements by Europeans were built in 1836, and the first house was built by a settler named William Fenwick on the south side of Diamond Lake. The first …Fremont Township is a township in Lake County, Illinois, USA. As of the 2020 census, its population was 33,422. The land of the township was first settled by Europeans in 1835, and the first permanent settlements by Europeans were built in 1836, and the first house was built by a settler named William Fenwick on the south side of Diamond Lake. The first post office named was established in the township was in 1839 between Half Day and McHenry, until it was disestablished in 1842. The post office was named after its postmaster, Charles Darling.