Dan Purdy went close for the visitors just past the hour after he beat Lims keeper to the ball inside the box but his cross was cut out by Limerick captain Pat Purcell.
At the other end, man-of-the match Rory Gaffney drove an excellent ball from Joe Gamble inches wide, with Town keeper Craig Hyland well beaten.
Jeffrey Judge then fired a Sean Brosnan cross off the underside of the bar and down onto the line with Lims appeals for a goal dismissed by the assistant referee.
Judge hit the post again from inside the box immediately after the break following a Shane Tracy cross and a neat layoff from Rory Gaffney.
The draw maintains Lims lead at the top, but on the balance of chances, the Shannonsiders, who forced 12 corners, will see this as two points dropped against their nearest challengers.
LIMERICK FC: Ryan, Kelly, Purcell, Kluciar (Treacy 60) Tracy, Gamble, McGann, Brosnan (Bradley 73) Judge, Foley (Behan 70), Gaffney.
LONGFORD TOWN: Hyland, Haverty, Lee, Hope, McDonagh, Bayly (Kirby 64) Gillespie, Purdy (Salmon 64) Bermingham, Shaw, Crawley (Griffith 70)
Referee: K Callinan (Cork).