Resident Population in Lewis and Clark County, MT was 75.01100 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Lewis and Clark County, MT reached a record high of 75.01100 in January of 2023 and a record low of 33.28100 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Lewis and Clark County, MT - last updated from the United States Federal Reserve on May of 2024.