Due to the low rainfall and marginal conditions the first settlers did not arrive in the area until the 1860s. The land around Lock was initially held as pastoral leases. This meant that for a very low rental (around ten shillings per square mile) pastoralists could graze sheep on vast areas of land relying entirely on natural vegetation rather than any attempts at pasture improvement.
This process of land settlement occurred south of Lock as early as the 1861 when Price Maurice took up 26 sq. miles of land which he retained until 1888. Over the next thirty years the pastoral leases slowly extended north towards the present site of Lock. By 1884 some 401 sq. miles of pastoral leases in the area were being run by six graziers. All leases had either expired, been surrended or been abandoned by 1893 and two years later the area was officially proclaimed. The problem, as with most of the Eyre Peninsula, was the lack of reliable surface water.
A major change occurred in the area with the arrival of the railway line from Port Lincoln in 1913. The area was serviced by a siding known simply as Terre Siding after one of the local properties. This was changed when the town was gazetted on 28 February 1918 and named Lock after Corporal Albert Lock, a member of the South Australian Survey Department who had been killed in Belgium on 9 October 1917.
The railway opened up the area's wheat growing potential but still the problem of low rainfall persisted. The problem was finally resolved in 1926 when the pipeline from the Tod Reservoir was turned on. Ironically two years later it was found that Lock was located above a huge underground water supply which could provide nearly 7 million litres of fresh water per day.