It lies on the A4076 road approximately midway between Haverfordwest and the port of Milford Haven and is served by Johnston railway station. Until the end of the 19th century, anthracite was mined here. The village is now a dormitory for Haverfordwest and Milford Haven. The parish church has the typical tall, slim castellated tower of churches in the largely English-speaking south of Pembrokeshire, sometimes known as "Little England beyond Wales".
Johnston was founded as a small farming and mining village sometime before 1801 when 99 people lived in the village. Maps from 1579 show Johnston as an already established village. The population steadily grew to 600 in 1951 and almost doubled in the next 10 years to 1,133. Since then Johnston has had a steady population growth.
Johnston is a majority Christian village with 62.4 per cent of people identifying as Christian, 0.2 per cent as Buddhist, 0.4 per cent as Muslim, 0.5 per cent as "Other" and 26.5 per cent as having no religion. 9.7 per cent of people did not state a religion.
The majority of people, 72.8 per cent, were born in Wales. 23.5 per cent were born elsewhere in the United Kingdom (22 per cent in England, 1.3 per cent in Scotland and 0.2 per cent in Northern Ireland). 0.3 per cent were born in Ireland; 1.2 per cent were born in countries that were members of the EU before 2001 while 0.4 per cent were born in EU countries that joined after 2001. 1.9 per cent were born in 'other countries'.
Johnston is not an ethnically diverse village with 99.55 per cent of the population identifying as White; 59.8 per cent identify only as Welsh and 6.7 per cent as Welsh and British. 12.7 per cent identify only as English while 1.2 per cent identify as English and British and 1 per cent identify as English and "other". 0.8 per cent identify as Scottish only while 0.2 per cent identify as Scottish and British, and 0.2 per cent as Scottish and "other". 0.2 er cent identified as Northern Irish only. 15.5 per cent identify only as British, while 8.7 per cent identify as British and "other". 75.8 per cent have no British identity while 32.5 per cent have no Welsh identity, and 1 per cent identify as Welsh and "other".
In 2011 11.4 per cent of inhabitants could speak Welsh, down from 13.81 per cent in 2001, but 18.5 per cent had some Welsh language ability. This is lower than the overall percentage for Pembokeshire and Wales, which are 19.2 and 19.0 respectively.
Johnston Community Council, has limited control over aspects of the running of the village.
Johnston CP School is a primary school with year groups, Nursery to Year 6. It has over 150 pupils. In 2017 it moved into a newly built building, previously it had been on its former site for approximately 30–35 years. Before then it was at another site in the north of Johnston.
Pupils in Secondary Education are automatically enrolled in Tasker-Milward V.C. School, in nearby Haverfordwest. Although parents may opt out of this and send their child to another school.
Johnston is served by 9 bus stops, six main with three smaller stops. Buses run to Haverfordwest, Milford Haven, Pembroke, Pembroke Dock, Neyland and Tenby.
Johnston railway station serves as a railway link. Trains run in both directions every 2 hours, with two main termini being Milford Haven railway station and Manchester Piccadilly station. The station itself is unmanned and is a request stop.
The Anglican church of St Peter, in the Diocese of St David's and established as a mission church in 1894, became a Chapel of Ease to Saint Paul's Church, Pentre Broughton in 1908. It is a grade II* listed building 
A meetinghouse for The Church of Jesus Christ of Latter-day Saints (LDS Church) was opened in December 2012 and is home to the Milford Haven Branch.
A greyhound racing track existed in the village. It opened in August 1934 and was trading in 1948 but the regularity of the racing in unknown. In 1948 and 1949 the Licensing Authorities listed the track as having a attendance capacity of just 200 which is the smallest known attendance of any track. The racing was independent which means unaffiliated to the sports governing body at the time (the National Greyhound Racing Club).
- "Community population 2011". Retrieved 19 April 2015.
- "PENBROK comitat". The British Library. British Library. Retrieved 9 September 2015.
- http://www.neighbourhood.statistics.gov.uk/dissemination/LeadTableView.do?a=7&b=6503117&c=Johnston&d=14&e=62&g=6491685&i=1001x1003x1032x1004&m=0&r=1&s=1361996529976&enc=1&dsFamilyId=2479[dead link]
- http://www.neighbourhood.statistics.gov.uk/dissemination/LeadTableView.do?a=7&b=6503117&c=Johnston&d=14&e=62&g=6491685&i=1001x1003x1032x1004&m=0&r=1&s=1361996529976&enc=1&dsFamilyId=2478[dead link]
- http://www.neighbourhood.statistics.gov.uk/dissemination/LeadTableView.do?a=7&b=6503117&c=Johnston&d=14&e=62&g=6491685&i=1001x1003x1032x1004&m=0&r=1&s=1361997984092&enc=1&dsFamilyId=2529[dead link]
- "GENUKI: Johnston". Retrieved 26 April 2015.
- "Church of St Peter, Johnston". British Listed Buildings. Retrieved 29 December 2013.
- Barnes, Julia (1988). Daily Mirror Greyhound Fact File, page 417. Ringpress Books. ISBN 0-948955-15-5.
- Particulars of Licensed tracks, Licensed Dog Racecourses. Licensing Authorities. 1948.
- Particulars of Licensed tracks, table 1 Licensed Dog Racecourses. Licensing Authorities. 1949.